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The capability of graphene to generate hot electrons is predicted to be effective in converting low energy photons into electrical currents for the mid-infrared photodetection [1,2]. However, the quantum yield of such hot electrons is not sufficient due to the limited thickness of two-dimensional graphene [3-5]. Therefore, it raises the question whether the electron thermalization is efficient enough to generate a large number of hot electrons in graphitic materials as a detectable photocurrent. Here, an experimental demonstration of the sufficient hot electron generation in Bernal stacking sequence nano-graphite films is presented. A comprehensive layer number dependence (1–120-layers graphene) study verifies the strong hot electron scattering correlations, exhibiting intriguing two-dimensional properties into their bulk counterparts. Consequently, the spectral coverage of hot electrons promoted from mid-infrared (4 μm) to near-infrared (1.2–1.6 μm) energy level is achieved, leading to a 109 eV−1 cm−2 populated hot electron density for the mid-infrared photodetection. In addition, the consistently increased number of photo-excited electrons via stacking of graphene layers, results in a gradual evolution of subsequent electron thermalization. The proposed scheme for exploring the thickness dependence electron thermalization property of the graphitic material paves the way to design ultrafast and sensitive mid-infrared photodetecters. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitroindoles show distinct T 1 state properties and applications. • 3HN-6NO 2 exhibits strong oxidizing, can generate radicals. • Dual reaction pathways identified in protic solvents. • Acidity and basicity critically influence 3HN-6NO 2 reactions. • Findings enhance understanding of nitroindoles in biosystems. Indoles are notable for their distinct photophysical and photochemical properties, making them useful indicators in biological systems and promising candidates for a variety of pharmaceutical applications. While some indoles exhibit room temperature phosphorescence, such a phenomenon has not been observed in nitroindoles. Typically, adding of a nitro group into aromatic compounds promotes ultrafast intersystem crossing and increases the formation quantum yield of the lowest excited triplet (T 1). Therefore, understanding the reactivity of nitroindoles′ T 1 states is imperative. This study investigated the physical properties and chemical reactivities of the T 1 state of 6-nitroindole (3HN-6NO 2) in both polar aprotic and protic solvents, using transient absorption spectroscopy. Our results demonstrate the basicity and acidity of 3HN-6NO 2 , emphasizing its potential for protonation and dissociation in mildly acidic and basic conditions, respectively. Furthermore, 3HN-6NO 2 has a high oxidizing capacity, participating in electron transfer reactions and proton-coupled electron transfer to produce radicals. Interestingly, in protic solvents like alcohols, 3HN-6NO 2 dissociates at the –NH group and forms N-H...O hydrogen-bonded complexes with the nitro group. By identifying transient absorption spectra of intermediates and quantifying kinetic reaction rate constants, we illuminate the unique properties of the T 1 state nitroindoles, enriching our understanding of their photophysical and photochemical behaviors. The results of this study have significant implications for their potential application in both biological systems and materials science. [ABSTRACT FROM AUTHOR]

[Display omitted] • The preparation strategy of integrated W-P/MoS 2 was developed by utilizing W doping engineering induced S v. • Modulating the photoelectric properties of MoS 2 via defect and doping engineering were analyzed. • DFT investigated the defect energy levels of S v introduced by tungsten doping in MoS 2. • The nonlinear optical and OL performance of W-P/MoS 2 was obtained at femtosecond time domain. Modulating the photoelectric properties of molybdenum disulfide (MoS 2) through defect engineering and heterometal doping is crucial for its potential applications in electronic and optoelectronic devices. Herein, a comprehensive overview is provided on the advancements of two-dimensional materials with a ternary structure comprising sulfur (S), molybdenum (Mo), and tungsten (W) in the field of optoelectronic device. A ternary W-P/MoS 2 (P: direct current target power) nanomaterial was designed and synthesized using W interior doping engineering induced S vacancies. The experimental results reveal that the introduction of W metal causes lattice distortion in MoS 2 , leading to the formation of S vacancies within W-P/MoS 2. Compared to pure MoS 2 , W-P/MoS 2 with S vacancies demonstrates enhanced reverse saturable absorption and optical limiting. Density functional theory calculations suggest that the S vacancies introduced by W doping in MoS 2 introduce defect energy levels, which are believed to be the reason for the improved nonlinear optical (NLO) performance of W-P/MoS 2. Furthermore, transient absorption spectroscopy reveals the photophysical model of carrier relaxation and presents an explanation for the optimized NLO properties of W-P/MoS 2. This work provides a novel strategy for the design and synthesis of ternary transition metal dichalcogenides and modulating the NLO properties by doping transition metal-mediated vacancies. [ABSTRACT FROM AUTHOR]

Incorporating plasmonic nanocrystals (NCs) into solid-state electronics is an important step toward realizing nanophotonic devices. However, only a few noble metal-based systems can directly precipitate plasmonic NCs in a solid transparent medium. In contrast, plasmonic metal oxide NCs can exhibit a plasmonic response at infrared energies that noble metal-based systems cannot reach due to their high carrier concentration. Here we demonstrate the precipitation of bismuth-doped ZnO (BZO) NCs in an aluminosilicate glass matrix, demonstrating a robust near-infrared (NIR)-localized surface plasmon resonance. Benefited from the strong resonant absorption by the plasmonic BZO NCs, these glass ceramics (GCs) exhibit enhanced ultrafast nonlinear optical (NLO) response across the NIR optical communication bands, which might be promising for applications such as optical limiting, optical switching, optical modulation, and NIR-nanophotonic devices. • This work reports the successful precipitation of plasmonic Bi-doped ZnO nanocrystals in an aluminosilicate glass. • These nanocrystals exhibit a robust localized surface plasmon resonance in the infrared region. • The plasmon response of the precipitated nanocrystals contributes to notably enhanced nonlinear optical characteristics. [ABSTRACT FROM AUTHOR]

Integrating interface engineering and precious heterometal doping with semiconductors is a feasible pathway to construct efficient charge transfer and improve the nonlinear optical (NLO) performance of materials. Here, we report a bimetallic selenide type-II heterostructure of Cu 3 Se 2 /WSe 2 (CWS) with a simple one-step magnetron co-sputtering of Cu and WSe 2 targets at low argon flow rates. Se first nucleates and precipitates to form nanospheres at low flow rates. Due to the electronegativity of Cu being greater than that of W and Cu prioritizes attachment to the outside of the Se nanospheres and promotes the formation of the nanorods-grown Cu 3 Se 2. A combined analysis of X-ray photoelectron spectroscopy and X-ray diffraction data was used to investigate the minor shift in the W 4 f/Se 2p ratio revealing that electrons shifted from Cu 3 Se 2 to WSe 2. The diffraction peaks of CWS and the valence electronic structure of Cu1+/Cu2+ confirmed the implantation of Cu 3 Se 2 nanorods on WSe 2. The NLO properties of CWS composite films were modulated by varying the power of Cu. More importantly, the nonlinear absorption coefficient of the CWS composite films formed after Cu 3 Se 2 promotion is much better than that of other unmodified pure WSe 2 films. The photogenerated carrier dynamics of CWS composite films were investigated by femtosecond transient absorption spectroscopy, and density functional theory calculations show that CWS composite films inhibit efficient electron transfer photogenerated carrier complexation. This work proposes a few strategies for designing heterogeneous structures with interface engineering and precious metal doping to promote adjustable electron transfer dynamics and achieve high NLO conversion efficiency. [Display omitted] • Single-step magnetron sputtering was used to synthesize and control growth of Cu 3 Se 2 /WSe 2 (CWS) composite films. • Interface engineering and heterometal doping CWS composite films for efficient charge transfer was analyzed. • The nonlinear absorption and transient absorption properties of CWS composite films were analyzed. [ABSTRACT FROM AUTHOR]

The ultrafast optical nonlinearity of an azonaphthalene derivative, hydroxy naphthol blue (HNB) disodium salt, is investigated using transient absorption spectra (TAS) and Z-scan technique. Reverse saturable absorption (RSA) is observed within the resonant absorption band, which is usually dominated by ground-state bleaching (GSB) and stimulated emission (SE) in most organic compounds. This observation indicates a remarkably strong excited-state absorption (ESA) in HNB. Global analysis of TAS suggests an ultrafast conversion from saturable absorption (SA) to RSA, which is assigned to the internal conversion from locally excited (LE) state to the first singlet (S 1) state. Further Z-scan study verifies the above results and reveals another intensity-depend SA-RSA transition, indicating increased S 1 population under strong laser irradiation. The calculated value of third-order nonlinear absorption coefficient at 650 nm, 190 fs is determined as 1.23 × 10−12 m/W. These studies demonstrate significant potential of azonaphthalene in ultrafast laser protection if further modulation of excited-state absorption can be achieved. • The ultrafast optical nonlinearity of HNB is studied by TAS and Z-scan. • RSA in resonant absorption region is observed due to extremely strong ESA on first excited state. • Mechanism of intensity-depend SA-RSA transition is investigated. [ABSTRACT FROM AUTHOR]

The device performance of novel solar cell configurations with porphyrin, hybrid perovskite-based materials as sensitizers depends on the interfacial processes and engineered interfaces with characteristic material properties can be fabricated employing energetic ion implantations. In this experimental work, the dye adsorption, optical absorption and interfacial electron injection in N719 sensitized Ag − , Au − , sequentially impinged and O 2 annealed titania films were studied. Prior to the dye sensitization process, impinged samples were fabricated employing mono-ion type, sequential implantations and a set of the as-implanted films were annealed at 450 °C for 1 h in O 2 environment. The N719 molecules are adsorbed onto Ag − , Au − impinged films through SCN ligands, indicated by the appearance of new Raman modes ν (Ag-S), ν (Au-S) respectively. The 1MLCT, 3MLCT bands of the dye molecules are altered upon implantation and annealing processes. A fast interfacial electron injection process with τ 2 ∼ 3.7 ps has been observed in the sensitized annealed sequentially impinged film at 6 × 1015 ions cm−2 (sensitized pristine TiO 2 exhibits τ 2 ∼ 51 ps) and is attributed to Ag − , Au − implants introducing new states to the conduction band of anatase TiO 2. The ability of ion-implantation technique to introduce new states to the band structure of materials has enormous significance in photo-catalytic, water-splitting, solar cell and hot electron injection technologies. [Display omitted] • Ball and stick representations of Ag − and Au − implanted TiO 2 matrix. • New Raman modes ν (Ag-S), ν (Au-S) respectively observed in N719 sensitized Ag − , Au − as-implanted, annealed films. • Tuning 1MLCT, 3MLCT bands of N719 molecules in sensitized as-implanted, annealed films. • Fast electron injection τ 2 ∼ 3.7 ps observed in sensitized annealed sequentially impinged film at 6 × 10 15 ions cm − 2. • Modified morphology of TiO 2 upon implantation and annealing processes. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS 2) has attracted much attention in the field of optoelectronic materials due to its stability and adjustable bandgap structure. However, improving the optoelectronic properties of MoS 2 is still a challenging research. Herein, Al doped MoS 2 (AMS) films were prepared by a simple single-step magnetron sputtering method. The bonding modes of Al implantation and auxiliary MoS 2 were investigated by adjusting metal Al anchoring. The successful synthesis of AMS films was confirmed by the analysis of X-ray diffraction and X-ray photoelectron spectroscopy measurements to investigate the diffraction peaks of Al and Al 2 S 3 and the valence electron structures of Al3+. Compared to MoS 2 , the A 1g Raman peaks of AMS films are slightly blue-shifted, and the peak positions of both Mo3d and S2p are slightly shifted towards higher binding energies. This is attributed to the surface plasmon resonance effect produced by Al doping resulting in a large amount of electron transfer to the conduction band (CB) of MoS 2. In addition, the density functional theory calculations reveal that Al doping of MoS 2 results in a higher concentration of electrons in CB of MoS 2 , the band gap of MoS 2 can be adjusted by changing the doping concentration of Al. The Z-scan results illustrated that MoS 2 was converted from saturable absorption to reverse saturable absorption (RSA) by adjusting the sputtering power of Al. This is attributed to the fact that Al doping increases the electron concentration in the CB of MoS 2 , which promotes the RSA of the excited states and doping energy levels of AMS films. The values of the nonlinear absorption coefficients of AMS films are 2–5 times higher than those of MoS 2 , which significantly improves the nonlinear absorption performance of MoS 2. The carrier relaxation process and kinetic mechanism of AMS films were investigated by transient absorption spectroscopy, moderate doping of Al can effectively improve the carrier lifetime. This implies that AMS films have good optoelectronic properties and have a wide application potential in optoelectronic devices. [Display omitted] • Single-step was used to synthesize and control the growth of MoS 2 nanosheets via metal Al anchoring. • Interface engineering and heterometal doping AMS films for efficient charge transfer was analyzed. • Promoting the optoelectronic and nonlinear optics properties of AMS films was analyzed. [ABSTRACT FROM AUTHOR]

• Synthesized thin films of halide perovskites with triple cations (Bi, Pb, Na/K) at B-site. • Exhibited good absorption coefficient, good charge carrier lifetime. • Unraveled ultrafast carrier dynamics using femtosecond transient absorption studies. • Faster free electron-hole recombination process found in FKBPI compared to FNBPI. • Degradation studies carried out by XRD, UV–Vis, TCSPC and DSC-TGA over 15 days. • Multiple cations in B-site produced stable organometallic halide photovoltaics. ABX 3 perovskites offer the advantage of manipulating its properties by introducing multiple cations in B-site. Over the years, researchers used mixed B-site perovskites in oxide electronics to tune their electrical, magnetic properties. Here we used the triple cations at B-site in formamidinium based organometallic halide perovskite solar cell (PSC) in order to improve its degradation behavior with respect to heat and moisture. We synthesized halide based two hybrid perovskites viz., formamidinium sodium bismuth lead iodide [NH 2 CHNH 2 (Na 0.25 Bi 0.25)Pb 0.5 I 3 and formamidinium potassium bismuth lead iodide [NH 2 CHNH 2 (K 0.25 Bi 0.25)Pb 0.5 I 3 using solution chemistry. In order to decrease the content of toxic lead in these perovskites, trivalent bismuth was incorporated in the Pb-site. Monovalent sodium and potassium were used to maintain the charge neutrality of B-site, which has the formal valence of + 2 in these ABI 3 type perovskites. Both of these perovskites showed reasonable optical band gaps with good charge carrier lifetime suggesting it as potential candidates for solar energy conversion and provisionally we achieved power conversion efficiency η = 0.52%. Moreover, superior thermal and moisture stability in these perovskites were observed in periodical structural and spectral analysis carried out by XRD, UV–Vis spectroscopy, time-correlated single photon counting (TCSPC) over the period of one month. Furthermore, ultrafast carrier dynamics in these perovskites were unraveled using femtosecond transient absorption studies. Our transient absorption kinetics data suggested more auger recombination and faster free electron-hole recombination process in FKBPI compared to FNBPI, which corroborates well with better energy conversion efficiency obtained in FNBPI based solar cell. [ABSTRACT FROM AUTHOR]

Alloying strategy in quantum dots (QDs) has shown great advantages in regulating photophysical properties and improving the performance of photovoltaic devices. Typically, CdSeTe alloy QD is proved to be a superior photosensitizer, and has presented great potential in constructing high-efficient quantum dot solar cells. However, systematic analysis for the carrier dynamics is still lacking. In this paper, the carrier dynamics within CdSeTe colloidal QDs and at the TiO 2 /CdSeTe interface has been studied in detail by transient absorption (TA) spectroscopy and photoluminescence (PL) spectroscopy. TA results show that the gradient component of CdSeTe QDs leads to different electronic transition properties distinct from those of their parent binary components. Temperature-dependent time-resolved PL spectra for the CdSeTe/TiO 2 demonstrate that PL lifetime decreases from 13.54 to 3.08 ns with increasing temperature from 10 to 300 K. Moreover, the electron transfer rate increases more quickly when temperature exceeds 250 K. In addition, it is confirmed that the crystallization characteristics of TiO 2 have a significant impact on the interfacial carrier dynamics. A faster electron transfer from CdSeTe QDs to rutile TiO 2 (R–TiO 2) has been obtained than that to anatase TiO 2 (5.65 × 108/s vs 3.21 × 108/s). Both QDs adsorption and electron transfer properties closely dependent on the crystal orientation of R–TiO 2 single crystal. CdSeTe QDs attached to the (100) R–TiO 2 single crystal surface achieve the fastest electron transfer rate than other R–TiO 2 orientations of (111), (110) and (001). [ABSTRACT FROM AUTHOR]

Quasi-two-dimensional (Q-2D) layered perovskite with alternating cations in the interlayer space (ACI) is a potential candidate for highly efficient and environmental stable solar cells. Here, we report the fabrication of photovoltaic devices using a novel layered Q-2D perovskite (AcA)MA n Pb n I 3n+1 (n = 4) containing acetamidinium (AcA+) and methylammonium (MA+) cations as spacer. With introducing appropriate amount of methylammonium chloride (MACl) as an additive in precursor solution, (AcA)MA 4 Pb 4 I 13 film presents micrometer sized crystalline grain and high crystalline quality, resulting in more than 40% enhancement of power conversion efficiency (PCE) compared to that without additive. Specially, an optimized (AcA)MA 4 Pb 4 I 13 device achieves the best PCE of 15.04% and retains more than 85% of the original PCE after 30 days under ambient condition (∼ 40% relative humidity, 25 ℃) without encapsulation, while there is no sign of degradation for accompanying (AcA)MA 4 Pb 4 I 13 film. Using ultrafast transient spectroscopy, we find that MACl additive in precursor solution results in slower charge transfer from small n phase to 3D-like phases in (AcA)MA 4 Pb 4 I 13 film, while there is no photoluminescence observed from small n materials; thus we may deduce that electrons and holes are separated efficiently in small n phases as well. We believe our results not only demonstrate that AcA+ can act as an effective spacer cation fabricating perovskite for efficient solar cells, but also help to understand the unique working mechanism of ACI perovskites in-depth. • With the appropriate amount of MACl achieved a highest PCE of 15.04%. • The PCE remains ∼ 90% for 30 days and the XRD shows no sign of change. • With MACl additive shows "slower" charge transfer. • Charge carriers are well-separated in small n materials of multi-phase ACI film. [ABSTRACT FROM AUTHOR]

[Display omitted] • Particle swarm optimization automates global fitting of time resolved spectral data. • Particle swarm optimization eliminates manually setting initial parameters in conventional fitting. • Automation makes global analysis efficient and accessible for non-experts. Time-resolved spectroscopy, especially transient absorption spectroscopy (TAS), provides valuable insights to excited state dynamics. Analyzing TAS data involves fitting complex kinetic traces at various probe wavelengths using different rate equations. Conventional TAS global fitting methods require domain experts to establish physically valid models and provide good initial guesses to generate converged solutions. This poses challenges for non-experts who seek to utilize TAS, thus limiting its broader application and impact. To address this problem, we propose an intelligent optimization framework based on the particle swarm optimization (PSO) algorithm. In the proposed method, the PSO algorithm acts as the global fitting method to find the optimal values of the target variables or unknown parameters in the kinetics models. The target solution is optimized by iteratively updating candidate solutions with respect to an objective feedback signal. We demonstrated the effectiveness of the proposed PSO-based global fitting method with both synthetic and experimental datasets. The results show that our proposed method can successfully find the optimal target values in the global fitting process automatically, thus eliminating the iterative manual labor traditionally required. The proposed intelligent optimization framework provides a novel approach for automatic global fitting of TAS data, which significantly enhances the accessibility and utilization of the TAS methodology. [ABSTRACT FROM AUTHOR]

Femtosecond laser, compared to continuous wave (c.w.) or nanosecond laser, has shown great promise in diversities of frontier applications because of its extremely short pulse width, high peak power and low thermal effect. In order to obtain femtosecond laser output, the design of suitable saturable absorber (SA) materials as a nonlinear modulation device is a key issue for a given laser system. However, the previous SA materials are limited in inorganic semiconductors, which have some constraints such as narrow working wavelength ranges, complex preparation process and high cost. By contrast, organic semiconductors have high molecular design freedom, good flexibility, simple preparation process, and low cost, and would act as an ideal SA material. Here, we report a novel strategy to tune and realize the femtosecond laser out by employing an organic small molecule SA of (Z)-2-(4-(pyrene-1-yl) phenyl)-3-(4-(1,2,2-triphenylvinyl) phenyl) acrylonitrile (Py-TPE). We show that Py-TPE has an ultrafast excited carrier relaxation time less than 20 ps, shorter than most of inorganic semiconductor materials. More importantly, by depositing such Py-TPE on the surface of tapered fiber as an SA device in Er-doped fiber laser system, an ultrafast fiber laser output with a pulse width as narrow as 447 fs and good stability was realized. This is the first report, to the best of our knowledge, to achieve femtosecond laser by taking advantage of the Py-TPE with ultrafast excited carrier relaxation time. These results demonstrate that Py-TPE is a novel organic saturable absorption material with great potential application in ultrafast laser and photonics. • Py-TPE shows an ultrafast excited carrier relaxation time (<74.8 fs) in the near-infrared region. • The use of Py-TPE SA in fiber lasers results in an exceptionally low threshold (30 mW) for mode-locking due to its low saturation intensity (20.61 MW/cm2). • The Er-doped mode-locked fiber laser based on Py-TPE SA has pretty narrow pulse width (447 fs) and good stability. [ABSTRACT FROM AUTHOR]

A photoactive MOF-based composite with simultaneously incorporated Ru-photosensitizer and Ni(II) molecular catalyst via a "ship-in-a-bottle" synthetic strategy, exhibits highly active, selective and robust, for photocatalytic CO 2 to CO conversion under visible-light illumination. Photocatalytic reduction of CO 2 to CO is a promising strategy for reducing atmospheric CO 2 levels and storing solar radiation as chemical energy. Here, we demonstrate that a molecular catalyst [NiII(bpet)(H 2 O) 2 ] successfully encapsulated into a highly robust and visible-light responsive metal–organic framework (Ru-UiO-67) to fabricate composite catalysts for photocatalytic CO 2 reduction. The composite Ni@Ru-UiO-67 photocatalysts show efficient visible-light-driven CO 2 reduction to CO with a TON of 581 and a selectivity of 99% after 20-h illumination, because of the facile electron transfer from Ru-photosensitizer to Ni(II) active sites in Ni@Ru-UiO-67 system. The mechanistic insights into photoreduction of CO 2 have been studied based on thermodynamical, electrochemical, and spectroscopic investigation, together with density functional theory (DFT) calculations. This work shows that encapsulating molecular catalyst into photoactive MOF highlights opportunities for designing efficient, stable and recyclable photocatalysts. [ABSTRACT FROM AUTHOR]

The photoexcited processes in two compounds belonging to the salicylidene-p-X-anilines family were investigated by time resolved absorption and emission spectroscopy in the femto-to-millisecond time domain. The studies were conducted in two solutions of different polarity and were supplemented by investigations in solid state (microcrystalline powder). In the polar solvent, both compounds share similar fluorescence properties. In the non-polar solvent, one of the compounds exhibits only the tautomeric emission, while for the other compound, the fluorescence is almost quenched, but still visible as a co-existence of the normal and tautomeric emissions. These different emission characteristics in a non-polar solvent were correlated with the aggregate formation. From femto– to miliseconds, various deactivation channels and conformers of the known tautomeric forms have been evidenced altogether with an additional fluorescence relaxation appearing only in molecular aggregates. A complete and detailed image of the photochromic cycles emerges by correlating structural dynamics with the experimentally observed kinetic and spectroscopic parameters over 10 orders of magnitude time-scale. • The photophysical properties two Schiff bases have been studied by time resolved spectroscopy. • The photochromic cycles and the de-activation mechanism of excited states were drawn. • An additional fluorescence relaxation appears only in molecular aggregates. • Two simultaneous processes take place in excited state: E -enol → Z -enol isomerization and the very fast proton transfer. [ABSTRACT FROM AUTHOR]

Graphical abstract We explore detail dynamics of stationary and static regimes of electron transfer between MBP and aromatic amines employing ultrafast time resolved fluorescence and absorption spectroscopy along with state-of-art data analysis methods and successfully demonstrate that transient absorption spectroscopy determines the bimolecular quenching rates (k d , M−1 s−1) instead of primary or intrinsic ET rate in diffusion control regime. Highlights • ET dynamics between MBP and aromatic donors are explored in diffusion control regime as well as non-diffusive regime. • Femtosecond time resolved fluorescence and fs TA replicate to each other leading to determine bimolecular quenching rates (k d , M−1 s−1) instead of primary or intrinsic ET rate in diffusion control regime. • Femtosecond time-resolved emission and fs TA studies along with global and target analysis determines the primary/intrinsic ET rates (k et) between excited MBP and studied donors. • Intrinsic ET rates (k et ∼1011 s−1) are found to be with very high and the process lies in Marcus normal region and back electron transfer occurs three order lower (k bet ∼108 s−1), the process lies in Marcus inverted region. • Driving force dependence of intrinsic charge separation (CS) and charge recombination rates (CR) shows Marcus bell-shape structure. Abstract Determination of primary/intrinsic electron transfer rate (k et = 1/τ et , s−1) in bimolecular photoinduced electron transfer reactions (PET) in solution phase monitoring fluorescence quenching is a controversial issue, predominantly due to constraint imposed by diffusion, and measurement of rate of formation of transient intermediates, therefore primary electron transfer rate, was suggested (J. Phys. Chem. B 2015, 119, 11253 − 11261). Herein, we report electron transfer dynamic of excited 7-methylbenzo[a]pyrene (MBP) in acetonitrile (ACN) in presence of different aromatic amine donors from very low concentration to finally in neat donors to access intrinsic, diffusion free, rate constants of bimolecular PET by using steady state and femtosecond time resolved fluorescence and femtosecond transient absorption (fs TA) spectroscopy. It appears that in lower concentration of donors, diffusion control or stationary regime of ET, observed dynamics by time resolved fluorescence as well as transient absorption spectroscopy replicate to each other leading to determine the bimolecular quenching rates (k d , M−1 s−1) instead of primary or intrinsic ET rates. In very higher donor concentration or in neat donors, non-diffusive or intrinsic regime of ET, amalgamation of femtosecond time-resolved emission and fs TA studies along with global and target analysis determines the primary/intrinsic ET rates (k et) between excited MBP and studied donors which are one to two orders of magnitude larger than corresponding bimolecular quenching rate constants (k d) in ACN. Intrinsic electron transfer occurs with very high rate of k et (∼1011 s−1) and the process lies in Marcus normal region and back electron transfer occur very slow k bet (∼108 s−1), the process lies in Marcus inverted region. [ABSTRACT FROM AUTHOR]

Highlights • Two π-conjugated pyrene derivatives were synthesized successfully. • The benzene peripheral substituent enhance the third-order optical nonlinearity. • The difference phenomenon for excited-state lifetime between both compounds. • Detailing description on transient absorption to interpret the dynamic process. Abstract In this work, two pyrene derivatives with delocalized π-electron system 1-(pyren-1-yl)−3-(5-Chlorothiophene-2-yl)acrylic ketone (1612) and 1-(pyren-1-yl)−3-(5-Phenylthiophene-2-yl) acrylic ketone (1613) were synthesized. The third-order nonlinear optical (NLO) response of these compounds dissolved in DMSO were investigated using Z-scan technique with 190 fs laser pulses at 532 nm. Large two-photon absorption was found for the two compounds, while the NLO response of 1613 was larger than 1612. The femtosecond transient absorption (TA) results demonstrate that both compounds have broad TA absorption band over the visible regime. Compared to 1612 , the TA band of 1613 exhibit a 15-nm blue shift of its peak while its UV–Vis absorption peak have 50 nm red-shift. Meanwhile, the TA decay curve also show that the excited-state lifetime of 1613 is longer, indicating the substituent group functionalization also has a significant impact on the excited-state relaxation processes. Our results show that both the NLO response and photo-physical dynamics of pyrene chromophores are readily tunable via peripheral substituent group, which is essential for the development of novel NLO materials based on this conjugated molecules. [ABSTRACT FROM AUTHOR]

A series of novel β -diketonate Eu3+ complexes with minor variations in the chemical structure of the diketone ligand were systematically studied. Six Eu3+ coordination compounds based on β -diketones, bearing linear perfluorinated substituents of various length (C1, C2, C3 and C6) and fixed pyrazole moiety were obtained. In addition, two water molecules, 1,10-phenanthroline or 4,7-diphenyl-1,10-phenanthroline as an ancillary ligand in compounds with fixed β -diketone ligand were used. Their photophysical properties were investigated by UV–Vis absorption and time-resolved femtosecond transient (fs-TA) absorption spectroscopy techniques. In this study, we investigate the impact of ancillary ligands and the fluorinated chain length of β-diketone ligands on the ultrafast relaxation processes that occur in the ligand environment. Relying on the ultrafast transient absorption measurements, it was demonstrated that the extension of fluorinated chains of β -diketone ligand leads to decrease of first excited singlet and triplet states relaxation rates. The compound with excessively long chain C 6 F 13 exhibits the slowest relaxation of the triplet state T 1. Besides, variation in the ancillary ligand alters the electronic energy transfer pathways in the whole complex. It was established, that introducing 4,7-diphenyl-1,10-phenanthroline (bath) instead of 1,10-phenanthroline (p hen) dramatically changing the electronic energy transfer dynamics in the whole coordination compound. On the basis of the fs-TA measurements we conclude the bath ligand act as acceptor of electronic energy of diketone ligand in the excited state. [Display omitted] • Ultrafast dynamics in the Eu3+ complexes were investigated by the fs-TA technique. • Experimental data on T 1 energy were supported by theoretical calculations. • The influence of fluorinated chains length on the processes of ISC and ligand-to-ion charge transfer was estimated. [ABSTRACT FROM AUTHOR]

Composite type photocatalyst F-TiO 2 /(N,C)-TiO 2 consisted of anatase-type TiO 2 with fluorine-doping (F-TiO 2 ) and TiO 2 with nitrogen and carbon-doping ((N,C)-TiO 2 ) was prepared by simple physical mixing to exhibit higher visible-light responsive photocatalytic nitrogen oxide (NO x ) decomposition activity than those of F-TiO 2 and (N,C)-TiO 2 . Transient absorption measurement clarified that the composite possessed longer carrier lifetime compared to that of each material (F-TiO 2 or (N,C)-TiO 2 ), resulting in higher photocatalytic activity. In the composite, photoexcited holes and electrons, which are not in impurity level but in valence and conduction band, respectively, should photocatalytically decompose NO x , judging from the redox potential of O 2 /O 2 ･− and the band positions of F-TiO 2 and (N,C)-TiO 2 . The mechanism for higher visible-light photocatalytic activity, or longer carrier lifetime can be explained by charge transfer between F-TiO 2 and (N,C)-TiO 2 through their impurity levels. The charge transfer should make photoexcited carries spatially separated to enhance the photocatalytic activity. [ABSTRACT FROM AUTHOR]

Abstract By using a graphene layer as fast carrier combination channel for WS 2. Graphene-WS 2 heterostructures be used as an example to study the charge transfer across the interface via transient absorption measurements. We found the transfer of photo-induced carriers from WS 2 to graphene take place within 83 fs, this ultrafast transfer time supports the charge transfer mechanisms via layer-coupled states and Coulomb field. Our results provide the basic information for understanding the photo-induced carriers transfer across the interfaces of van der Waals heterostructures and suggest that van der Waals heterostructures may be useful in ultrafast optoelectronic devices. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Time-resolved diffuse reflection spectra were recorded for rutile-type TiO 2 powders. • Global and target analysis was applied for all the observed data-set. • Spectral shape of surface carriers and their time evolution have intimate relation in the water-oxidation activities. Abstract We studied the correlation between carrier characters and water oxidation activity of commercially available rutile-type TiO 2 powders by global and target analysis of time-resolved transient diffuse reflection spectra. The whole observed data-set were well fitted by the target analysis using three independent components. Spectral shape of surface carriers and their time evolution obtained by the target analysis have intimate relation in the water-oxidation activities. A series of this type of investigation will contribute to the breakthrough of the material design for promising photocatalyst. [ABSTRACT FROM AUTHOR]

Abstract Two novel conjugated pyrene derivatives (C1 and C2) with D- π -A structures were synthesized to realize broadband reverse saturable absorption (RSA) under femtosecond laser excitation (ranging from 515 to 700 nm) resulting from two-photon absorption (TPA) and TPA-induced excited-state absorption. Furthermore, these two derivatives showed RSA on the picosecond and nanosecond time regions (532 nm). Quantum chemical calculations indicated that two mechanisms for the HOMO-LUMO excitation of the two molecules exist simultaneously: intramolecular charge transfer (which is considered to trigger the nonlinear optical response) and π-π* transition. It was found that the π-π* transition localized in the pyrene group can contribute to the increase in the nonlinear absorption of pyrene derivatives. Femtosecond time-resolved transient absorption spectrum provided information on the dynamics of the locally excited singlet state (1LE) and the charge-transfer state (1CT) for both compounds. The results show that these pyrene derivatives are promising candidates for future optoelectronic and RSA applications. Highlights • Two novel pyrene derivatives were synthesized to systematically investigated the nonlinear optical properties. • Both compounds showed reverse saturable absorption under the excitation of different pulse widths (fs, ps and ns). • Femtosecond transient absorption revealed the ultrafast dynamics. • The π-π* transition localized in the pyrene group can contribute to the increase in the nonlinear absorption properties. [ABSTRACT FROM AUTHOR]

A series of spectroscopic measurements were performed on membrane fractions and detergent-solubilized complexes from the green sulfur bacterium (GSB) Chlorobaculum (Cba.) tepidum . The excitation migration through the entire GSB photosynthetic apparatus cannot be observed upon excitation of membranes in the chlorosome region at 77 K. In order to observe energy transfer from the Fenna-Matthews-Olson (FMO) protein to the reaction center (RC), FMO was directly excited at ~800 nm in transient absorption experiments. However, interpretation of the results is complicated by the spectral overlap between FMO and the RC. The availability of the Y16F FMO mutant, whose absorption spectrum is drastically different from that of the WT, has enabled the selection of spectral regions where either only FMO or the RC contributes. The application of a directed kinetic modeling approach, or target analysis, revealed the various decay and energy transfer pathways within the pigment-protein complexes. The calculated FMO-to-RC excitation energy transfer efficiencies are approximately 25% and 48% for the Y16F and WT samples, respectively. [ABSTRACT FROM AUTHOR]

Three linear push-pull compounds comprised of difluoroboron β-diketonate and triphenylamine unit 4,6-Bis(4-(diphenylamino)phenyl)-2,2-difluoro-2H-1,3,2-dioxaborinin-1-ium-2-uide, (E)-6-(4-(Diphenylamino)phenyl)-4(4(diphenylamino)styryl)-2,2-difluoro-2H-1,3,2-dioxaborinin-1ium-2-uide and 4,6-Bis((E)-4-(diphenylamino)styryl)-2,2-difluoro-2H-1,3,2-dioxaborinin-1-ium-2-uide (ABA, ABVA, and AVBVA) have been probed by many spectroscopies. The results clarify the photo-physical property of the compounds where ABVA and AVBVA are linked with vinyl units (V). The solvent-dependent steady absorption and photoluminescence spectra data shows that the vinyl unit and the polarity of the solvent influence the photo-physical properties of the compound. Moreover, the vinyl unit would further enhance the role of the polar environment. The transient absorption measurement then offers excitation relaxation behavior. The results show that excited compounds in cyclohexene go back to the ground state through the intramolecular charge transfer (ICT) state, and the transfer lifetime from the initial excited state to the ICT state would prolong after the introduction of vinyl unit. The relaxation behavior becomes complex when cyclohexene is replaced by tetrahydrofuran. Some excited compounds go directly back to the ground state and others go back to the ground state after passing through the ICT state. In addition, two-photon PL measurements and a Z-scan technique are employed, and this confirms that these compounds have two-photon behavior, but the two-photon absorption section gradually decreases. This decrease is attributed to the spectral shifting affected by the vinyl unit. [ABSTRACT FROM AUTHOR]

Injection of photoexcited electrons in the para-Ethyl Red dye to TiO 2 nanoparticles (Anatase, 40 nm diameter) is characterized by transient absorption on ultrafast time scales. This study focuses on understanding the effect of aprotic solvents on the injection rate. Transient absorption at 1900 cm −1 is probed following a 400 nm pulse which excites the electronic transition of p-ER adsorbed on TiO 2 through its carboxylic group. Measurements conducted in three different solvents show that electron injection lifetimes are in the 250–300 fs range but display a trend in correlation with solvent polarity: the electron injection lifetime is the shortest (257 fs) in acetonitrile followed by dichloromethane (271 fs) and chloroform (296 fs). This trend can be understood by using the Marcus theory in which the reorganization energy varies correspondingly in the three different solvents. This study shows that for aprotic solvents the one with the highest polarity facilitates the fastest electron injection. [ABSTRACT FROM AUTHOR]

Thermoelectric battery is effective in converting thermoelectricity based on Seebeck effect. As an all-solid-state energy conversion model, this battery is highly significant in improving the utilization of solar energy using a clean and noiseless process. However, efficient photothermal conversion and temperature difference control are the key challenges in enhancing solar-thermal-electric conversion. Herein, we constructed a novel sunlight-driven thermoelectric system with temperature difference control characteristic. In which the light-driven phase change heat storage material (PCHSM) was used as the hot side, and the phase change cool storage material (PCCSM) as the cold side. Ultrafast photothermal conversion of the PCHSM was achieved through the nonradiative decay of the excited state, which was revealed by means of femtosecond transient absorption technique. Solar radiation was efficiently utilized as shown by the excellent visible light absorption, ultrafast photothermal transformation, and phase change heat storage characteristics of the PCHSM. The PCCSM with high phase change cool storage performance could provide enough cold energy to maintain the cold-side temperature. Temperature gradient was controlled using the cold-side and hot-side materials based on the phase-change temperature control characteristics. [ABSTRACT FROM AUTHOR]

The paper presents a brief overview of the role of metal hydride complexes in understanding the dynamics of hydrogen generation in homogeneous water reduction catalysts. In addition, the kinetics of protonation of [Os(phen) 2 (CO)(H)] + and the one-electron reduced form of the complex, [Os(phen)(phen − )(CO)(H)], in acetonitrile solution were examined. The monocationic complex reacted with tosylic acid to form a distinct intermediate species which was found to be a dihydrogen complex; this went on to produce hydrogen and the solvento complex. The one-electron reduced complex was prepared by reduction of the photoexcited monocationic complex with the sacrificial donor BIH. Protonation of the reduced complex by tosylic acid occurred with a rate constant approximately 100 million times larger. The results are used to address possible mechanistic pathways of existing homogeneous catalysts. [ABSTRACT FROM AUTHOR]

The carrier dynamics of the semiconductor photocatalyst is the essential concern to clarify the detailed mechanisms of photocatalytic water splitting reactions, which is one of the key issues of artificial photosynthesis to produce solar fuels. In this present study, time-resolved transient diffuse reflection spectra of rutile type TiO 2 powder were recorded. Singular value decomposition against whole observed spectral data-set that was followed by global and target analysis has been performed for the first time. A series of examination revealed that the carriers generated in the bulk of TiO 2 particle and two distinctive surface carriers are decaying with their own lifetimes. Moreover, the comparison of the measurements both in vacuum and under oxygen atmosphere suggested that the lifetime of surface holes is several tens of nanoseconds. The factors that govern the activity of photocatalyst should be precisely addressed based on thus identified spectral and lifetime features of carriers. Therefore, the present investigation is expected to open the new door to give some good hints when designing more active photocatalysts. [ABSTRACT FROM AUTHOR]

The catalytic transformation of carbon dioxide into fuels is one of the most important reactions for creating a sustainable, carbon-neutral energy economy. Given that the sun is the only plausible energy source that can accommodate the increased global energy demand without contributing to catastrophic climate change, it makes sense to use solar energy to drive this reaction, ideally using the largest possible portion of the solar spectrum. Over the past several years, we have explored the use of reduced rylenediimide chromophores, which absorb wavelengths ranging into the near-infrared, as strongly reducing photosensitizers capable of photosensitizing Re(diimine)(CO) 3 L metal centers towards the binding and reduction of CO 2 . We have explored the effects of varying the binding geometry, donor–acceptor redox potentials, and excitation wavelength on the kinetics of electron transfer from the reduced rylenediimide to the metal center. So far, we have achieved charge-separated lifetimes in electrocatalytically active complexes of 25 ns when illuminated with near-infrared light, and >250 ns when illuminated with blue light. [ABSTRACT FROM AUTHOR]

Through comparing the linear and nonlinear optical property of two pull-push chromophores, which are composed of difluoroboron β-diketonate functionalized with carbazole and tert-butyl carbazole, the role of tert-butyl in chromosphere has been discussed in detail. The tert-butyl unit would lead to the absorption and fluorescence peak red shift and accelerate the fluorescence relaxation rate of chromophores. Moreover, the tert-butyl unit would affect obviously the two-photon optical property of chromophore according to the Z-scan test. The transient absorption (TA) data shows that these two pull-push chromopphores both own intramolecular charge transfer (ICT) characteristics and the tert-butyl unit accelerate the dynamic rate of ICT generation and relaxation process, which may be responsible for the variance of fluorescence property. [ABSTRACT FROM AUTHOR]

The shape of nanocrystals can effectively adjust their photo-physical properties, which becomes a route to improve the nanocrystal-based semiconductor device. Herein, we further dig the photo-physical properties of CsPbBr 3 hexagonal nanocrystals (HNCs), in which CsPbBr 3 cubic nanocrystals (CNCs) serves as a reference. It is found that the activity of carrier in CsPbBr 3 HNCs is higher than that of CsPbBr 3 CNCs, owing to the slow energy dissipation path related to the phonon energy, which slows down the carrier temperature cooling process and accelerate the carrier recombination behavior simultaneously. Moreover, the spin flip process may occur in the CsPbBr 3 HNCs, whose lifetime is longer than that of CsPbBr 3 CNCs owing to the weakening of phonon scattering of Elliott-Yafet mechanism. In addition, the photoluminescence test of CsPbBr 3 HNCs in optical fiber microcavity shows that its light wave-guiding performance is determined by the self-absorption effect and the conventional light wave-guiding effect, which are both super to those of CsPbBr 3 CNCs, benefiting from its high PL quantum yield. Our research suggests that the CsPbBr 3 HNCs exhibits a huge potential in the field of optoelectronics, spintronics and photo-communication. • Based on the laser spectroscopy, the carrier dynamics of CsPbBr 3 hexagonal nanocrystals (HNCs) has been clearly analyzed. • By employing the circular transient absorption technique, the lifetime of spin flip dynamics in CsPbBr 3 HNCs is ∼3.43 ps. • The light wave-guiding effect of CsPbBr 3 HNCs is affected by the self-absorption effect and the light propagation effect. [ABSTRACT FROM AUTHOR]

Here we report a new member of in-plane anisotropic 2D materials Rhenium Diselenide (ReSe 2) which holds a stable distorted 1 T' phase with its relatively narrow bandgap to explore the in-plane anisotropic structural, electrical, and optical properties. The proposed polarization-sensitive photodetectors based on few-layer ReSe 2 provides highly anisotropic photodetection behavior with linearly dichroic ratio up to ≈2.62 under 808 nm illumination. We measured carrier transport in space and time by mapping carrier density in a ReSe 2 plate using transient absorption microscopy. These results directly determined the carrier diffusion coefficients of about 4100 cm2 s-1 and 2900 cm2 s-1 along the armchair and zigzag directions, respectively, providing fundamental parameters to better understand the anisotropy of ReSe 2 and promote future 2D optoelectronic applications in polarization-sensitive detection. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) are the most promising candidate for next-generation photovoltaics. The carrier dynamics behavior in perovskite is closely related to the performance of the solar cell. Particularly, manipulating the hot carriers has the potential to achieve ultrahigh-efficiency solar cells beyond the conventional Shockley-Queisser efficiency limit. Therefore, it is crucial to study and understand the carrier transport process in perovskite. However, the carrier dynamics behavior in the femtosecond time scale is difficult to be detected. Nowadays, femtosecond transient absorption techniques address this challenge effectively. We summarize the monitoring of hot carriers cooling, trapping of defect states, and charge transfer process after photoexcitation of PSCs by transient absorption and analyze the effective utilization of carriers in these processes. Finally, an outlook that will encounter in its future development is provided. • Extending hot carrier cooling lifetime to break the Shockley-Queisser limit. • Analyze of defect passivation and charge extraction in perovskite solar cells. • Transient absorption technique for studying carrier dynamic on femtosecond to nanosecond time scales. [ABSTRACT FROM AUTHOR]

Photosystem II in oxygenic organisms is a large membrane bound rapidly turning over pigment protein complex. During its biogenesis, multiple assembly intermediates are formed, including the CP43-preassembly complex (pCP43). To understand the energy transfer dynamics in pCP43, we first engineered a His-tagged version of the CP43 in a CP47-less strain of the cyanobacterium Synechocystis 6803. Isolated pCP43 from this engineered strain was subjected to advanced spectroscopic analysis to evaluate its excitation energy dissipation characteristics. These included measurements of steady-state absorption and fluorescence emission spectra for which correlation was tested with Stepanov relation. Comparison of fluorescence excitation and absorptance spectra determined that efficiency of energy transfer from β-carotene to chlorophyll a is 39 %. Time-resolved fluorescence images of pCP43-bound Chl a were recorded on streak camera, and fluorescence decay dynamics were evaluated with global fitting. These demonstrated that the decay kinetics strongly depends on temperature and buffer used to disperse the protein sample and fluorescence decay lifetime was estimated in 3.2–5.7 ns time range, depending on conditions. The pCP43 complex was also investigated with femtosecond and nanosecond time-resolved absorption spectroscopy upon excitation of Chl a and β-carotene to reveal pathways of singlet excitation relaxation/decay, Chl a triplet dynamics and Chl a → β-carotene triplet state sensitization process. The latter demonstrated that Chl a triplet in the pCP43 complex is not efficiently quenched by carotenoids. Finally, detailed kinetic analysis of the rise of the population of β-carotene triplets determined that the time constant of the carotenoid triplet sensitization is 40 ns. • Absence of CP47 prevents association of CP43 with the D1 or D2 proteins. • Spectroscopic studies on preassembly CP43 complex (pCP43) at 293 K and 77 K • Excited-state dynamics of pCP43-bound chlorophyll (Chl) a and β-carotene studied. • Carotenoid triplet sensitization inefficiently quenches Chl a triplet in pCP43. [ABSTRACT FROM AUTHOR]

[Display omitted] We applied transient absorption spectroscopy to study the early photodynamics in a system composed of CdTe quantum dots (QDs) and cytochrome c (Cyt c) protein. In the QDs and Cyt c mixtures, about 25 % of the excited QD electrons quickly relax (∼23 ps) to the ground state and roughly 75 % decay on slower time scale – mostly due to quenching by Cyt c. On the basis of the assumed model, we estimated the contribution of electron transfer and other mechanisms to this quenching. The primary quenching mechanism is probably energy transfer but electron transfer makes a significant contribution (∼8 %), resulting in photoreduction of Cyt c. The lifetime of one fraction of reduced Cyt c (35–90 %) is ∼ 1 ms and the lifetime of the remaining fraction was longer than the ∼ 50-ms time window of the experiment. We speculate that, in the former fraction, the back electron transfer from the reduced Cyt c to QDs occurs and the latter fraction of Cyt c is stably reduced. [ABSTRACT FROM AUTHOR]

Two push-pull compounds, which are comprised of triphenylamine (TPA) (electron donor units) and functionalized β-diketones difluorboron complexes (electron acceptor units) are probed by many spectroscopies, which offers the relationship between electron acceptor and the intrinsic excited state properties of push–pull chromophores. We found that the photoluminescence (PL) intensity would enhance with the number of electron acceptor. Transient absorption (TA) data shows that intramolecular charge transfer (ICT) process really exists in the two molecules after photoexcitation and this process would be prolonged through increasing the electron-acceptor, which would be responsible for the improvement of PL property. [ABSTRACT FROM AUTHOR]

We discuss the influence of spectral filtering by samples in femtosecond transient absorption measurements. Commercial instruments for transient absorption spectroscopy (TA) have become increasingly available to scientists in recent years and TA is becoming an established technique to measure the dynamics of photoexcited systems. We show that absorption of the excitation pulse by the sample can severely alter the spectrum and consequently the temporal pulse shape. This “spectral self-filtering” effect can lead to systematic errors and misinterpretation of data, most notably in concentration dependent measurements. The combination of narrow absorption peaks in the sample with ultrafast broadband excitation pulses is especially prone to this effect. [ABSTRACT FROM AUTHOR]

A series of 4′-phenyl-2,2′:6′,2″-terpyridyl Pt(II) chloride complexes bearing different aryl substituents ( 1a – 1f ) was designed and synthesized. The photophysical properties of these complexes have been systematically investigated. All complexes exhibit strong 1 π , π * absorption bands in the UV region; and broad, structureless metal-to-ligand charge transfer ( 1 MLCT) absorption bands in the visible region. When excited at the charge-transfer absorption band, the complexes exhibit room temperature luminescence ( λ em = 555–614 nm) in CH 3 CN. The emissions of complexes 1c – 1f with electron-donating or extended π -conjugation substituents are assigned to the 3 MLCT states. Meanwhile, the emitting state of 1a and 1b exhibits a significant intraligand 3 π , π * character. Complexes 1a – 1d exhibit moderate triplet transient absorptions from visible to NIR region, where reverse saturable absorption (RSA) occurs. Their photophysical properties have been investigated with the aim to provide a basis for elucidating the structure-property correlations and developing new nonlinear optical materials. [ABSTRACT FROM AUTHOR]

Betalains are natural dyes which can be used in non-toxic environmentally friendly dye-sensitized solar cells (DSSC). In this paper we provide results characterizing the performance of DSSC constructed using betanin, 2,17-bidecarboxybetanin, vulgaxanthin I and betanidin-6- O -(6′,6″-di- O - trans -4-coumaroyl)- β -sophoroside, as well from the red beetroot aqueous extract. The photovoltaic parameters of the cells correlate with the results of time-resolved measurements for fully assembled cells. We reveal that insufficient electron injection quantum yield is mainly responsible for the limited sunlight conversion efficiency. In betacyanin-based DSSC, only about 50% of the excited dye molecules inject electrons, while the rest suffer from a dye S 1 fast internal conversion process. In betaxanthin-based DSSC, the quantum yield of electron injection is higher (about 70%), but the total sunlight conversion efficiency is smaller due to the blue-shifted absorption band. A probable explanation of the differences in the electron injection quantum yields in the studied dyes is that of different rates of the competing S 1 →S 0 internal conversion processes. [ABSTRACT FROM AUTHOR]

Nitrous acid (HONO) is an important tropospheric pollutant and a major source of hydroxyl radical in the atmospheric gas phase. However, studies on the role of HONO in atmospheric aqueous phase chemistry processes are relatively few. The present work investigated the photochemical reaction of HONO with triclosan (TCS), which is an emerging contaminant, using a combination of laser flash photolysis spectrometry and gas chromatography mass spectrometry. With these techniques, the reaction pathway of HONO with TCS was proposed by directly monitoring the transient species and detecting the stable products. ·OH was generated from the photodissociation of the HONO aqueous solution and attacked TCS molecules on different sites to produce the TCS-OH adducts with a second-order rate constant of 1.11 × 10 9 L mol −1 s −1 . The ·OH added a C atom adjacent to the ether bond in the aromatic ring of TCS and self-decayed when the ether bond broke. The intermediates generated from the addition of ·OH to the benzene ring of the TCS molecular structure were immediately nitrated by HONO, which played a key role in the formation process of nitrocompounds. An atmospheric model suggests that the aqueous oxidation of TCS by ·OH is a major reaction at high liquid water concentrations, and the photolysis of TCS dominates under low-humidity conditions. [ABSTRACT FROM AUTHOR]

This paper presents spectroscopic investigations of IsiA, a chlorophyll a -binding membrane protein produced by cyanobacteria grown in iron-deficient environments. IsiA, if associated with photosystem I, supports photosystem I in light harvesting by efficiently transferring excitation energy. However, if separated from photosystem I, IsiA exhibits considerable excitation quenching observed as a substantial reduction of protein-bound chlorophyll a fluorescence lifetime. Previous spectroscopic studies suggested that carotenoids are involved in excitation energy dissipation and in addition play a second role in this antenna complex by supporting chlorophyll a in light harvesting by absorbing in the spectral range inaccessible for chlorophyll a and transferring excitation to chlorophylls. However, this investigation does not support these proposed roles of carotenoids in this light harvesting protein. This study shows that carotenoids do not transfer excitation energy to chlorophyll a . In addition, our investigations do not support the hypothesis that carotenoids are quenchers of the excited state of chlorophyll a in this protein complex. We propose that quenching of chlorophyll a fluorescence in IsiA is maintained by pigment-protein interaction via electron transfer from an excited chlorophyll a to a cysteine residue, an excitation quenching mechanism that was recently proposed to regulate the light harvesting capabilities of the bacteriochlorophyll a -containing Fenna-Mathews-Olson protein from green sulfur bacteria. [ABSTRACT FROM AUTHOR]

A bipyridine phenothiazine ligand [(PTZEtv 2 bpy) and metal complexes [Ru(Ph 2 phen) 3 ] 2+ ( 1 ), [(Ph 2 phen) 2 Ru(PTZEtv 2 bpy)] 2+ ( 2 ), and [(PTZEtv 2 bpy)(Ph 2 phen)Ru(dpp)] 2+ ( 3 ) were synthesized and characterized, where Ph 2 phen is 4,7-diphenyl-1,10-phenanthroline, dpp is 2,3-bis(2-pyridyl)pyrazine and PTZEtv 2 bpy is 4,4′ ethylene bridged phenothiazine 2,2′bipyridine. The reduction potentials of PTZEtv 2 bpy, 1 , 2 , and 3 were determined by cyclic and square wave voltammetric methods. The absorbance and emission spectra of complexes 2 and 3 yield intense, visible Metal-to-Ligand Charge Transfer (MLCT) transitions. The nanosecond transient absorption data indicate formation of both the 3 MLCT state and a ligand localized 3 PTZ state. [ABSTRACT FROM AUTHOR]

A novel technique for testing the timing properties of scintillators is presented. The technique is based on transient absorption (TA) induced in a scintillating material by a selective excitation of the activator ion. A figure of merit to assess the timing properties of scintillators is suggested. This parameter was estimated for a set of cerium doped lutetium–yttrium oxyorthosilicate (LYSO:Ce) bars, which have been fabricated for Barrel Timing Layer sensor of Compact Muon Solenoid detector (CMS BTL) and exhibited different timing properties, and compared with the results obtained by conventional coincidence time resolution (CTR) measurements. The figure of merit applied for the tested bars shows a strong correlation (Pearson's correlation coefficient R = 0.95) with the CTR. These results suggest that the TA technique could be used as an experimental method to expand in a complementary way the extensive qualification procedure of LYSO:Ce crystals that will be performed for the production of the CMS BTL detector. • Coincidence time resolution correlates with activator population rise time. • Population rise time can be probed by transient absorption in femtosecond domain. • Transient absorption can be exploited for testing of scintillator timing properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3MeO-NN and 3Me-NN have comparable hydrogen abstraction and oxidation abilities. • 3MeO-NN has a rate towards proton three orders of magnitude faster than 3Me-NN. • The dimer of 2,2,2-trifluoroethanol participates in the reaction with 3MeO-NN. • 3MeO-NN forms a hydrogen-bonded complex in methanol solution. Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs), often found in polluted air, are carcinogenic and mutagenic. The nitro group increases the spin–orbit coupling and results in the lowest excited triplet (T 1) on the picosecond time scale with a high yield. The electron-donating substituents have a significant influence on the photophysics and photochemistry of nitro-PAHs. We used transient absorption spectroscopy and kinetic analysis to investigate the reactivities of the T 1 state 1-methoxy-4-nitronaphthalene (3MeO-NN) and 1-methyl-4-nitronaphthalene (3Me-NN). The results show that the methoxy and methyl substitutions have a minor effect on their hydrogen abstraction and electron accepting abilities. The main distinction is their reaction rates towards protons. The second order rate constant of 3MeO-NN towards protons is three orders of magnitude greater than that of 3Me-NN, indicating that 3MeO-NN has a stronger hydrogen bond accepting ability. The kinetic analysis reveals that the dimer of 2,2,2-trifluoroethanol participates in the reaction with 3MeO-NN. These results suggest that the formation of the hydrogen-bonded complex is responsible for the unusually short lifetime of 3MeO-NN in methanol solution and the lack of hydrogen abstraction radicals during the decay of 3MeO-NN in methanol. [ABSTRACT FROM AUTHOR]

• Excited state electron dynamics of novel Metalated porphyrins-napthalimide molecules was investigated by femtosecond transient absorption spectroscopy (fs-TAS). • The rate constants of excited states are estimated using the global analysis of the obtained fs-TAS data. • Long-lived triplet state (lifetime ∼10 μ s for PN-Zn) formed via intersystem crossing. • Open aperture z-scan at non-resonant excitation of 800 nm revealed strong three-photon absorption by these molecules. • The experimental second hyperpolarizability was estimated to be ∼10-31 esu and verified by DFT calculations. Porphyrin applications are primarily related to electronic transitions across a broad spectrum. In this context, understanding the excited state electron dynamics is necessary in such chromophores. Herein, we report the ultrafast photophysical characterization of one free base and three transition metallated porphyrin - napthalimide based donor - acceptor systems (PN-Fb , PN-Ni , PN-Cu , and PN-Zn) in dichloromethane (DCM) solution using transient absorption spectroscopy (TAS) in the spectral range of 430–780 nm by the Soret band excitation at 400 nm. The different rate constants were extracted using a target model analysis of the collected transient absorption spectra and established a consistent photophysical model of molecular excited state population relaxations. The photophysical model consisted of the following various processes: (a) internal conversion in the range of 215–400 fs, (b) vibrational relaxation in the range of 1.35–62 ps, and (c) singlet state relaxation times in the range of 0.17–2.06 ns, and finally (d) 0.03–10 μs was attributed to the triplet state lifetimes. We have also measured the nonlinear optical properties of these molecules by the open and closed aperture Z-scan studies, which was carried out by 800 nm, 70 fs photoexcitation. The theoretical fittings to the experimental data resulted in an effective three-photon absorption coefficient and positive nonlinear refractive index. Further, from the Z-scan data, the second hyperpolarizability of the molecules was calculated, and the values were 10 - 31 esu. Additionally, complete optimization of individual structures and construction of these PN systems was achieved using density functional theory (DFT) calculations and the obtained results were found to be consistent with the experimental observations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vermilion darkening process studied with a phase transformation. • Transient absorption spectroscopy applied to pigments degradation. • Cinnabar degradation is accelerated in presence of chlorine ions. The application of no destructive techniques in the field of Cultural Heritage is becoming fundamental to understanding degradation phenomena. In this study, Transient Absorption (TA) spectroscopy was exploited to explain the process which causes the darkening of Red Vermilion, a famous pigment known also as cinnabar. The optical properties involved in the process are studied in pure HgS and chlorine doped HgS samples, before and after exposure to UV light (365 nm). The study was carried out with particular attention on the ground state bleaching signals, directly connected to the formation of intra-gap trap levels responsible for the pigment degradation. First derivative reflectance spectra reveal the presence of these defectivities, while the analysis of Tauc plots from Kubelka Munk function confirms the reduction of energy band gap due to UV exposure. With the help of Density Functional calculations, we simulated the role of S vacancies in producing a defective alpha-phase, the consequent reduction of the energy band gap and, finally, the progressive phase transformation to the cubic metacinnabar. Transient Absorption turns out to be an important tool of diagnosis about the conservation state of pigments applied in the field of Cultural Heritage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Easy and efficient synthesis of rhodanine-3-acetic acid-linked structural isomers (RD1 and RD2) is reported. • An accurate method of calculating electron affinity (E a) based on exciton binding energy has been presented. • The values of ionization potential and electron affinity have been calculated using DFT as well as from electrochemical measurements to know about electron injection capability of dye molecules. • Electron transfer from excited state of the dye to TiO 2 nanoparticles has been demonstrated using time-resolved emission and transient absorption spectroscopy. The π spacer-acceptor (A) pair may play an important role in tuning properties of organic dyes. Hence, we developed alkyne-rhodanine-3-acetic acid (yne-rda) containing dyes with carbazole as a donor (D) unit. Out of the two developed isomeric dyes (RD1 and RD2) , RD1 possesses the D-π-A design whereas, RD2 is having π-D-A structure. By employing various spectroscopic and computational techniques, the optical properties of these dyes were studied, and we found that electron transfer (ET) from synthesized dyes to TiO 2 nanoparticles (NPs) is feasible. Furthermore, the femtosecond transient absorption measurements provided evidence of ET from dyes to TiO 2 NPs. [ABSTRACT FROM AUTHOR]

Cd element alloyed perovskite nanocrystals is an effective strategy to improve the photovoltaic performance. However, it still remains necessary to further explore the effect of Cd element in photo-physics and opto-eletronic performance. Here, the optoelectronic characteristics of Cd alloyed CsPbBr 3 nanocrystals (CsPb 1‒ x Cd x Br 3 NCs) is investigated systemically. With the incorporation of Cd element, the crystal structure passes through from cubic (x = 0.0) to hexagonal phase (x = 0.85). The linear absorption cross sections at 400 nm monotonically decrease with x increasing, while the two-photon absorption action cross section at 800 nm increases to the maximum of 5.7 × 105 GM at x = 0.10. Meanwhile, the thermal activation model perfectly explains the optoeletronic performance of prototype photodetectors based on CsPb 1‒ x Cd x Br 3 NCs whose photo-current and photo-responsivity reach the maximum at x = 0.27. Finally, the corresponding primitive flexible photodetector shows negligible change with the device bending. Our results offer a deep insight into the strategy of Cd element alloyed into perovskite nanocrystals and broaden their application in nonlinear optical imaging or photo-detector. • The CsPb 1‒ x Cd x Br 3 perovskite NCs were synthesized by hot injection method. • With the incorporation of Cd element, the crystal structure changes from cubic to hexagonal phase. • The thermal activation model perfectly explains the optoeletronic performance of prototype photodetectors based on CsPb 1‒ x Cd x Br 3 NCs. • The corresponding primitive flexible photodetector shows negligible change with the device bending. [ABSTRACT FROM AUTHOR]

The semiconductor La 5 Ti 2 CuS 5 O 7 (LTC) is a potential photocatalyst capable of operating under visible light irradiation and behaves both as a photocathode and anode when embedded onto metal layers. Time-resolved diffuse reflectance (TRDR) measurements were carried out on LTC powder and LTC deposited on Au as the back contact using the particle-transfer method. Results of TRDR measurements of powdered LTC indicated the existence of long-lived photo-excited carriers, and suggested the existence of a mechanism for preventing carrier loss in LTC. Prior research has reported that LTC has a rod-shaped crystal structure and that electrons and holes are transported through different, spatially separated channels. Based on this, we introduced a one-dimensional carrier transport model. By analyzing TRDR data, we extracted material parameters such as the diffusion coefficient of LTC. Theoretical results indicated that a micron-sized LTC particle would be preferable if carriers trapped at the top-surface do contribute to photocatalytic gas generation. [ABSTRACT FROM AUTHOR]

LHCSR3 is a member of the Light-Harvesting Complexes (LHC) family, which is mainly composed of pigment-protein complexes responsible for collecting photons during the first steps of photosynthesis. Unlike related LHCs, LHCSR3 is expressed in stress conditions and has been shown to be essential for the fast component of photoprotection, non-photochemical quenching (NPQ), in the green alga Chlamydomonas reinhardtii . In plants, which do not possess LHCSR homologs, NPQ is triggered by the PSBS protein. Both PSBS and LHCSR3 possess the ability to sense pH changes but, unlike PSBS, LHCSR3 binds multiple pigments. In this work we have analyzed the properties of the pigments bound to LHCSR3 and their excited state dynamics. The data show efficient excitation energy transfer between pigments with rates similar to those observed for the other LHCs. Application of an exciton model based on a template of LHCII, the most abundant LHC, satisfactorily explains the collected steady state and time-resolved spectroscopic data, indicating that LHCSR3 has a LHC-like molecular architecture, although it probably binds less pigments. The model suggests that most of the chlorophylls have similar energy and interactions as in LHCII. The most striking difference is the localization of the lowest energy state, which is not on the Chlorophyll a (Chl a) 610-611-612 triplet as in all the LHCB antennas, but on Chl a613, which is located close to the lumen and to the pH-sensing region of the protein. [ABSTRACT FROM AUTHOR]