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Incorporating photoactive linkers into metal–organic frameworks (MOFs) has proved useful in improving photophysical properties of organic chromophores. This is achieved by controlling the local packing of linkers or defect engineering within the MOF. Using these ideas, we demonstrate that a tetraphenylethylene-based MOF exhibits long-lived linker-based emission out to 1 μs—substantially longer than previously reported. The emission contains two independent components whose dynamics branch from early timescales. These findings suggest that charge recombination and distinct defect sites exist and contribute a weak yet detectable emission, and demonstrate how high-sensitivity transient photoluminescence spectroscopy can reveal unexpected populations in nominally crystalline materials. [ABSTRACT FROM AUTHOR]

A degenerated four‐wave‐mixing (FWM) process in single‐crystal (CH3NH3)PbBr3 (MAPbBr3) is reported, where 150‐fs laser pulses at 1.33 µm are employed as the pump. Two pump photons interact with a single crystal, producing another two photons with higher and lower energies, respectively. One of the FWM‐generation sidebands is tuned from ∼1.23 to 1.21 µm and the other from ∼1.43 to 1.48 µm for the center wavelength, as the pump fluence is increased from 2.6 to 11.69 mJ cm−2. The self‐phase modulation induced by the strong pump pulses through the optical Kerr effect is responsible for the tuning dynamics. Transient spectroscopy not only verifies the FWM scheme for the interacting waves but also reveals the interference dynamics between the FWM‐generated sidebands and the probe pulse. In particular, the angular dependence of the FWM generation supplies direct evidence for the phase‐matching geometry. Using experimental data, a nonlinear refractive index coefficient of 1.19 × 10−14 cm2 W−1 at 1.33 µm for single‐crystal MAPbBr3 is determined. [ABSTRACT FROM AUTHOR]

Recent years have witnessed an increasing interest in time‐dependent coupled‐cluster (TDCC) theory for simulating laser‐driven electronic dynamics in atoms and molecules, and for simulating molecular vibrational dynamics. Starting from the time‐dependent bivariational principle, we review different flavors of single‐reference TDCC theory with either orthonormal static, orthonormal time‐dependent, or biorthonormal time‐dependent spin orbitals. The time‐dependent extension of equation‐of‐motion coupled‐cluster theory is also discussed, along with the applications of TDCC methods to the calculation of linear absorption spectra, linear and low‐order nonlinear response functions, highly nonlinear high harmonic generation spectra and ionization dynamics. In addition, the role of TDCC theory in finite‐temperature many‐body quantum mechanics is briefly described along with a few other application areas. This article is categorized under:Electronic Structure Theory > Ab Initio Electronic Structure MethodsTheoretical and Physical Chemistry > SpectroscopySoftware > Simulation Methods [ABSTRACT FROM AUTHOR]

In this review, we have attempted to briefly summarize the influence of an external electric field on an assembly of tautomeric molecules and to what experimentally observable effects this interaction can lead to. We have focused more extensively on the influence of an oriented external electric field (OEEF) on excited-state intramolecular proton transfer (ESIPT) from the studies available to date. The possibilities provided by OEEF for regulating several processes and studying physicochemical processes in tautomers have turned this direction into an attractive area of research due to its numerous applications. [ABSTRACT FROM AUTHOR]

Transient spectroscopies are sensitive to charge carriers released from trapping centres in semiconducting devices. Even though these spectroscopies are mostly applied to reveal defects causing states that are localised in the energy gap, these methods also sense-charge from quantum wells in heterostructures. However, proper evaluation of material response to external stimuli requires knowledge of material properties such as electron effective mass in complex structures. Here we propose a method for precise evaluation of effective mass in quantum well heterostructures. The infinite well model is successfully applied to the InGaAsN/GaAs quantum well structure and used to evaluate electron effective mass in the conduction and valence bands. The effective mass m/m0 of charges from the conduction band was 0.093 ± 0.006, while the charges from the conduction band exhibited an effective mass of 0.122 ± 0.018. [ABSTRACT FROM AUTHOR]

[Display omitted] • New Type II visible photoinitiating systems (Vis-PIs) in solvent-free formulations were tested. • Low toxicity PAMAM dendrimers act as effective co-initiators replacing traditional amines. • Sunlight drives efficient radical polymerization after a few minutes of exposure. • An electron transfer mechanism is elucidated by transient spectroscopy. The performance of a series of visible-light driven photoinitiating systems (Vis-PIs) for radical polymerization was evaluated. The Vis-PIs formulations consisted of aqueous solutions containing xanthene dyes as sensitizers, while polyamido-amine (PAMAM) dendrimers were tested as alternative co-initiators of lower toxicity than the traditional amines. Acrylamide and HEMA were used as probe monomers and the respective polymers were characterized by FTIR, DSC and viscosimmetry. In order to elucidate the mechanism of photopolymerization, the triplet excited-states and semirreduced forms of the dyes were characterized by transient spectroscopy. Photophysical parameters as intersystem crossing and radical quantum yields were also determined for each dye/dendrimer couple. All Vis-PIs operated successfully under solar irradiation, achieving high monomer conversions after short exposure times. Interestingly, formulations with partially halogenated dyes showed the highest efficiency, which correlates inversely with the affinity and the electron transfer capability between the reactants. This study demonstrates the usefulness of dye/dendrimer combinations to operate as efficient aqueous Vis-PIs under an inexpensive, unlimited and natural energy source such as sunlight. [ABSTRACT FROM AUTHOR]

In this work we elucidate the main steps of the CO oxidation mechanism over Au/CeO2(111), clarifying the course of CO adsorption at a broad variety of surface sites as well as of transmutations of one CO species into another. By combining transient spectroscopy with DFT calculations we provide new evidence that the active centers for CO conversion are single gold atoms. To gain insight into the reaction mechanism, we employ Modulation Excitation (ME) DRIFT spectroscopy in combination with the mathematical tool of Phase Sensitive Detection to identify the active species and perform DFT calculations to facilitate the assignments of the observed bands. The transient nature of the ME-DRIFTS method allows us to sort the observed species temporally, providing further mechanistic insight. Our study highlights the potential of combined transient spectroscopy and theoretical calculations (DFT) to clarify the role of adsorbates observed and to elucidate the reaction mechanism of CO oxidation over supported gold and other noble-metal catalysts. [ABSTRACT FROM AUTHOR]

Time-resolved emission of [Ir(ppy)2dcbpy]Cl (1a, ppy = 2-phenylpyridine, dcbpy = 2,2′-bipyridine-5,5′-dicarboxylic acid) dissolved in DMF revealed a biexponential decay of the excited state. Prior studies on cyclometalated iridium complexes indicated that such dual emission behavior can be attributed to an impurity, compounds that have two LUMO states that are close in energy, or the presence of ion-pairing. To probe each of these effects, a series of homoleptic, Ir(ppy)3 (2), and heteroleptic complexes, [Ir(ppy)2dcbpy]X [X = PF6−(1b), BPh4−(1c)] and [Ir(ppy)2bpy]X [bpy = 2,2′-bipyridine, X = Cl− (3a) PF6−(3b)], were synthesized and photophysically characterized. Among these complexes, only 1a exhibited dual emission with the emission lifetimes of 430 ± 5 ns (80%) and 125 ± 6 ns (20%) in DMF. These lifetimes were further confirmed with the nanosecond transient absorption kinetics, indicating that the dual emission likely did not originate from an impurity. When probing the emission and absorption kinetics of the salts 1b and 1c only one lifetime of 550 ± 10 ns was observed, indicating that the short lifetime of the Cl− salt (1a) comes from a putative ion-paired complex. Density-Functional Theory (DFT) calculations on 1 and 2 fragments in DMF helped uncover the reason behind the ion-pair formation, with carboxyl substituents in 1a causing a loss in electron density on the 3,3′-position of dcbpy. Additionally, the loss in electron density was experimentally validated with 1H NMR, which showed a noticeable downfield shift of the 3,3′-protons in relative to the shifts in 1b and 1c. The data supports that the dual emission observed in 1a is not from two separately emissive states, rather from the dissociated and ion-paired complexes.

The precise quantification of the impact of photoluminescence reabsorption (PLr) in metal‐halide perovskite solar cells (PSCs) remains challenging. Herein, the PLr effect is examined by combined time‐resolved photoluminescence (TRPL) spectroscopy and time‐resolved terahertz spectroscopy (TRTS) and a model is proposed that relates both, the PLr and nonradiative recombination rate (knr) to the quasi‐Fermi‐level splitting (QFLS). PLr is shown to be beneficial for QFLS when the nonradiative recombination rate (knr) is below a critical value of ≈7 × 105 s−1; at high knr PLr is detrimental to QFLS. By incorporating PLr into a two‐diode model that allows extraction of the effective knr, the series resistance (rs), and the shunt resistance (rsh) in PSCs, it is found that neglecting PLr overestimates the effective knr, although it does not affect the value of rs and rsh. The findings herein provide insight into the impact of the PLr effect on metal‐halide PSCs. [ABSTRACT FROM AUTHOR]

Modern integrated devices and electrical circuits have often been designed with carbon nanostructures, such as carbon nanotubes (CNTs) and graphene due to their high thermal and electrical transport properties. These transport properties are strongly correlated to their acoustic phonon and carrier dynamics. Thus, understanding the phonon and carrier dynamics of carbon nanostructures in extremely small regions will lead to their further practical applications. Here, we demonstrate ultrafast time-resolved electron diffraction and ultrafast transient spectroscopy to characterize the phonon and carrier dynamics at the boundary of quasi-one-dimensional CNTs before and after Joule annealing. The results from ultrafast time-resolved electron diffraction show that the CNTs after Joule annealing reach the phonon equilibrium state extremely fast with a timescale of 10 ps, which indicates that thermal transport in CNTs improves following Joule annealing. The methodology described in this study connects conventional macroscopic thermo- and electrodynamics to those at the nanometer scale. Realistic timescale kinetic simulations were performed to further elaborate on the phenomena that occur in CNTs during Joule annealing. The insights obtained in this study are expected to pave the way to parameterize the unexplored thermal and electrical properties of carbon materials at the nanometer scale. Image 1 [ABSTRACT FROM AUTHOR]

The bis‐iodo β‐pyrrole‐substituted BF2‐chelated dipyrromethene, I2BODIPY, and its structural analogue BF2‐chelated aza dipyrromethene, I2azaBODIPY, carrying a nitrogen at the meso‐position instead of carbon, were synthesized and characterized as new set of triplet sensitizers using different techniques. These sensitizers were further functionalized with fullerene, C60, at the central boron atom to build donor‐acceptor conjugates. Using spectral, electrochemical, and computational methods, these conjugates were characterized, and the energy levels were established. Intersystem crossing to populate the triplet state was observed upon excitation of I2BODIPY and I2azaBODIPY, however, the measured rates of kISC were found to be nearly two orders of magnitude higher for I2azaBODIPY (kISC∼1011 s−1) compared to I2BODIPY (kISC∼109 s−1). The energetics, kISC, and position of HOMO and LUMO levels was found to control the ability of the dyad to undergo electron transfer, although the donor‐acceptor distances were virtually the same in both I2BODIPY‐C60 and I2azaBODIPY‐C60 conjugates. Free‐energy calculations revealed that the photoinduced electron transfer process was thermodynamically feasible from only the singlet excited states in both conjugates. Consequently, electron transfer from the 1I2BODIPY* in competition with intersystem crossing was witnessed in the case of I2BODIPY‐C60 dyad while in the case of I2azaBODIPY‐C60 dyad, excitation of azaBODIPY led to a short‐lived charge transfer state involving the catechol bridge followed by populating the low‐lying 3I2azaBODIPY* state without promoting the process of charge separation involving C60. The lifetime of the charge‐separated states was in the ns range in the I2BODIPY‐C60 conjugate both in polar and nonpolar solvents. [ABSTRACT FROM AUTHOR]

Photocatalytic water splitting by solar light is an environment‐friendly means for generating hydrogen as energy resources. For practical use, photocatalysts with higher activity are desired. Recently it was found that the photocatalytic activity of SrTiO3 is remarkably improved by Na‐doping. However, why Na‐doping enhances the activity has not been well understood. In this work, we found that Na‐doping in SrTiO3 introduces new mid‐gap states. Transient absorption measurements revealed that photoexcited electrons were trapped into these states within ∼20 ps after excitation. These trapped electrons have longer lifetime than those in undoped SrTiO3, and number of surviving electrons in microseconds increased ∼15 times. These electrons are trapped at the mid‐gap states, but still keep reactivity with reactant molecules. Furthermore, they were effectively captured by H2‐evolution cocatalyst, indicating that they can participate in steady‐state reactions. This work emphasizes the important role of electron‐trapping states introduced by doping on photocatalytic activity. [ABSTRACT FROM AUTHOR]

• Analytic methods to study the charge carrier dynamics are introduced. • The fates of charge carrier trapping and recombination are understood. • Various interfacial charge transfer processes are discussed case-by-case. Heterogeneous photocatalysis mediated by semiconducting TiO 2 has attracted continuous interest during the past decades and has shown great potentials in environmental remediation and solar energy conversion. Basically, photocatalysis is initiated by the TiO 2 excitation. The generated charge carriers undergo trapping, recombination, and interfacial transfer before proceeding the redox reaction at TiO 2 surface. Monitoring the charge carrier dynamics is of particulate importance for understanding the underlying mechanism and designing efficient photocatalysts. This review overviews the recent progress in characterization of charge carrier dynamics. We will present the analytic techniques for monitoring the fate of charge carriers at each elementary photocatalytic step, including charge carrier generation, trapping and recombination inside the photocatalyst, as well as the interfacial charge transfer. The charge carrier dynamics at TiO 2 /H 2 O interface, hole transfer reactions for O 2 production, and photocatalytic oxidation of organic compounds and nitric oxides, and electron transfer reactions for photocatalytic reduction of viologens and metal ions are addressed, aiming at a deeper understanding of photocatalytic process. [ABSTRACT FROM AUTHOR]

Molecular reactivity can change dramatically with the absorption of a photon due to the difference of the electronic configurations between the excited and ground states. Here we report on the discovery of a modular system (Schiff base formed from an aldehyde and an amine) that upon photoexcitation yields a more basic imine capable of intermolecular proton transfer from protic solvents. Ultrafast dynamics of the excited state conjugated Schiff base reveals the pathway for proton transfer, culminating in a 14‐unit increase in pKa to give the excited state pKa*>20 in ethanol. Ultrafast dynamics of the excited state conjugated Schiff base of a fluorene derivative reveals the pathway for proton transfer, culminating in a 14‐unit increase in pKa of the excited state, with a measured pKa*>20 in ethanol, yielding a "super" photobase. [ABSTRACT FROM AUTHOR]

Abstract: The interplay between nanomorphology and efficiency of polymer‐fullerene bulk‐heterojunction (BHJ) solar cells has been the subject of intense research, but the generality of these concepts for small‐molecule (SM) BHJs remains unclear. Here, the relation between performance; charge generation, recombination, and extraction dynamics; and nanomorphology achievable with two SM donors benzo[1,2‐b:4,5‐b]dithiophene‐pyrido[3,4‐b]‐pyrazine BDT(PPTh2)2, namely SM1 and SM2, differing by their side‐chains, are examined as a function of solution additive composition. The results show that the additive 1,8‐diiodooctane acts as a plasticizer in the blends, increases domain size, and promotes ordering/crystallinity. Surprisingly, the system with high domain purity (SM1) exhibits both poor exciton harvesting and severe charge trapping, alleviated only slightly with increased crystallinity. In contrast, the system consisting of mixed domains and lower crystallinity (SM2) shows both excellent exciton harvesting and low charge recombination losses. Importantly, the onset of large, pure crystallites in the latter (SM2) system reduces efficiency, pointing to possible differences in the ideal morphologies for SM‐based BHJ solar cells compared with polymer‐fullerene devices. In polymer‐based systems, tie chains between pure polymer crystals establish a continuous charge transport network, whereas SM‐based active layers may in some cases require mixed domains that enable both aggregation and charge percolation to the electrodes. [ABSTRACT FROM AUTHOR]

Abstract: The photochemical reactivity of 2‐hydroxymethylphenol (1) was investigated experimentally by photochemistry under cryogenic conditions, by detecting reactive intermediates by IR spectroscopy, and by using nanosecond and femtosecond transient absorption spectroscopic methods in solution at room temperature. In addition, theoretical studies were performed to facilitate the interpretation of the experimental results and also to simulate the reaction pathway to obtain a better understanding of the reaction mechanism. The main finding of this work is that photodehydration of 1 takes place in an ultrafast adiabatic photochemical reaction without any clear intermediate, delivering quinone methide (QM) in the excited state. Upon photoexcitation to a higher vibrational level of the singlet excited state, 1 undergoes vibrational relaxation leading to two photochemical pathways, one by which synchronous elimination of H2O gives QM 2 in its S1 state and the other by which homolytic cleavage of the phenolic O−H bond produces a phenoxyl radical (S0). Both are ultrafast processes that occur within a picosecond. The excited state of QM 2 (S1) probably deactivates to S0 through a conical intersection to give QM 2 (S0), which subsequently delivers benzoxete 4. Elucidation of the reaction mechanisms for the photodehydration of phenols by which QMs are formed is important to tune the reactivity of QMs with DNA and proteins for the potential application of QMs in medicine as therapeutic agents. [ABSTRACT FROM AUTHOR]

Recent advances in the use of transient absorption (TA) and time-resolved vibrational spectroscopies (TRIR and TR 3 ) to study both excited states and reaction intermediates in metal complexes and porphyrins which intercalate into DNA are reviewed. A particularly well-studied class of compounds, which nicely illustrates the comparative advantages of these techniques, is that of ruthenium dppz complexes where the complex might show light-switching or photo-oxidising behaviour depending on the nature of the ancillary ligand. Comparative data on Re- and Cr-dppz complexes are also considered. In the second part of this review transient studies of porphyrins, which are known to intercalate into DNA, are considered with particular emphasis on tetramethyl-pyridiniumporphyrins, where the photophysical behaviour of the metal-free and various metal derivatives are compared. [ABSTRACT FROM AUTHOR]

Gold nanoparticles with an average diameter of 10 nm, functionalized by the dye molecule rhodamine B isothiocyanate, have been synthesized. The resulting material has been extensively characterized both chemically, to investigate the bonding between the dye molecules and the nanoparticles, and physically, to understand the details of the aggregation induced by interaction between dye molecules on different nanoparticles. The plasmonic response of the system has been further characterized by measurement and theoretical simulation of the static UV–Vis extinction spectra of the aggregates produced following different synthesis procedures. The model parameters used in the simulation gave further useful information on the aggregation and its relationship to the plasmonic response. Finally, we investigated the time dependence of the plasmonic effects of the nanoparticles and fluorescence of the dye molecule using an ultrafast pump–probe optical method. By modulating the quantity of dye molecules on the surface of the nanoparticles it was possible to exert fine control over the plasmonic response of nanoparticles. [ABSTRACT FROM AUTHOR]

We have used time-resolved absorption and fluorescence spectroscopy with nanosecond resolution to study triplet energy transfer from chlorophylls to carotenoids in a protective process that prevents the formation of reactive singlet oxygen. The light-harvesting complexes studied were isolated from Chromera velia, belonging to a group Alveolata, and Xanthonema debile and Nannochloropsis oceanica, both from Stramenopiles. All three light-harvesting complexes are related to fucoxanthin-chlorophyll protein, but contain only chlorophyll a and no chlorophyll c. In addition, they differ in the carotenoid content. This composition of the complexes allowed us to study the quenching of chlorophyll a triplet states by different carotenoids in a comparable environment. The triplet states of chlorophylls bound to the light-harvesting complexes were quenched by carotenoids with an efficiency close to 100%. Carotenoid triplet states were observed to rise with a ~5 ns lifetime and were spectrally and kinetically homogeneous. The triplet states were formed predominantly on the red-most chlorophylls and were quenched by carotenoids which were further identified or at least spectrally characterized. [ABSTRACT FROM AUTHOR]

Many linked processes occur concurrently in strongly excited semiconductors, such as interband and intraband absorption, scattering of electrons and holes by the heated lattice, Pauli blocking, bandgap renormalization and the formation of Mahan excitons. In this work, we disentangle their dynamics and contributions to the optical response of a ZnO thin film. Using broadband pump-probe ellipsometry, we can directly and unambiguously obtain the real and imaginary part of the transient dielectric function which we compare with first-principles simulations. We find interband and excitonic absorption partially blocked and screened by the photo-excited electron occupation of the conduction band and hole occupation of the valence band (absorption bleaching). Exciton absorption turns spectrally narrower upon pumping and sustains the Mott transition, indicating Mahan excitons. Simultaneously, intra-valence-band transitions occur at sub-picosecond time scales after holes scatter to the edge of the Brillouin zone. Our results pave new ways for the understanding of non-equilibrium charge-carrier dynamics in materials by reliably distinguishing between changes in absorption coefficient and refractive index, thereby separating competing processes. This information will help to overcome the limitations of materials for high-power optical devices that owe their properties from dynamics in the ultrafast regime.

Upconverting NaErF 4 :Yb 3+ ,Gd 3+ nanoparticles (NPs) and nanorods (NRs) with improved red emission have been successfully achieved via a facile hydrothermal route using oleic acid as the assistant surfactant. The crystalline phase, morphology even the size are simultaneously tuned by controlling the reaction temperatures and Gd 3+ doping contents. The higher synthesis temperature leads to the morphology evolution from NPs to NRs. The integrated intensity ratio of red to green emissions is much improved for Gd 3+ codoping nanostructures. The microstructure characterizations along with the steady and transient spectroscopy are performed to better understand the underlying mechanisms of phase evolution and emission enhancement. For the different states of Er 3+ , i.e. 2 H 11/2 and 4 F 9/2 , the radiative/non-radiative transition probabilities could be affected by Gd 3+ doping in different ways as for NPs and NRs, based on the lifetime and emission intensity data. NaErF 4 :Yb 3+ ,Gd 3+ nanosctructures are expected to have promising applications in multimodal bioimaging for deeper tissue penetration. [ABSTRACT FROM AUTHOR]

A novel class of β-functionalized push-pull zinc opp-dibenzoporphyrins were designed, synthesized, and utilized as sensitizers for dye-sensitized solar cells. Spectral, electrochemical, and computational studies were systematically performed to evaluate their spectral coverage, redox behavior, and electronic structures. These porphyrins displayed much broader spectral coverage and more facile oxidation upon extension of the π conjugation. Free-energy calculations and femtosecond transient absorption studies (charge injection rate in the range of 1011 s−1) suggested efficient charge injection from the excited singlet state of the porphyrin to the conduction band of TiO2. The power conversion efficiency ( η) of YH3 bearing acrylic acid linkers ( η=5.9 %) was close to that of the best ruthenium dye N719 ( η=7.4 %) under similar conditions. The superior photovoltaic performance of YH3 was attributed to its higher light-harvesting ability and more favorable electron injection and collection, as supported by electrochemical impedance spectral studies. This work demonstrates the exceptional potential of benzoporphyrins as sensitizers for dye-sensitized solar cells. [ABSTRACT FROM AUTHOR]

Here, we report the synthesis, optical properties, and solid-state packing of monodisperse oligomers of diketopyrrolopyrrole (DPP) up to five repeating units. The optical properties of DPP oligomers in solution and the solid state were investigated by a combination of steady-state and transient spectroscopy. Transient absorption spectroscopy and time-correlated single photon counting (TCSPC) measurements show that the fluorescence lifetime decreases with an increase in the oligomer size from monomer to trimer, thereby reaching saturation for pentameric DPP oligomers. The solid-state packing and crystallinity were probed by using advanced techniques, which included grazing incidence small-angle X-ray scattering (GISAXS) and X-ray diffraction (XRD) to elucidate the structure-property trend. Collectively, our chain-length dependent studies establish the fundamental correlation between the structure and property and provide a comprehensive understanding of the solid-state properties in DPP-DPP based conjugated systems. [ABSTRACT FROM AUTHOR]

Free radical induced oxidation/reduction mechanisms of the hazardous water contaminant thiacloprid have been unravelled using pulse radiolysis techniques involving transient spectral analysis and redox titration experiments. The OH-induced oxidation of thiacloprid proceeds with appreciable rate, the reaction rate constant has been determined to be k OH = 4.8 × 10 9 mol −1 L s −1 . The OH attack leaves behind a rather complex free radical system consisting of ∼9% α-aminoalkyl radicals, ∼31% aminyl + aminium nitrogen centred radicals, ∼46% radicals at the sulfur and ∼14% hydroxycyclohexadienyl radical of the pyridyl moiety. Since ∼86% of radicals are formed on the key cyanoiminothiazolidine pharmacophore, OH is anticipated to be an appropriate candidate for inactivation of this biologically active pollutant. The one-electron reduction exerted by e aq − occurs at a diffusion controlled rate. As a result of the e aq − attack pyridinyl radical forms that takes part in subsequent protonation and dechlorination processes. The course of events is anticipated to lead to the destruction of another important part of the molecule in respect to insecticidal activity. [ABSTRACT FROM AUTHOR]

The use of transient vibrational spectroscopy in the analysis of rhenium(I) and ruthenium(II) complexes is discussed. Particular focus is given to the use of resonance Raman spectroscopy to probe initial photoexcitation and transient resonance Raman and infrared spectroscopy to observe subsequent relaxation processes. Several types of excited states are accessible for these systems, which can be probed on a range of timescales by these techniques. These include ligand-centered π,π*, intraligand chargetransfer, and metal-to-ligand charge transfer; a number of these states may be overlapping and show mixing. As such, these techniques are described in some detail and their utility is given by discussion of examples in which the electronic complexity of the system increases from systems which are metal-to-ligand charge-transfer through to systems which have complex interplay between intraligand and metal-to-ligand charge transfer states. Particular attention is paid to complexes containing [Re(CO) 3 (L)(N^N)] metal centers and dipyrido[3,2-a:2′,3′-c]phenazine ligands, as subtle structural changes on these often manifest in significant changes in the photophysical properties and they are therefore well-suited to the investigation of excited states. The use of these complexes in areas such as solar energy conversion and the probe of biological systems are also discussed. [ABSTRACT FROM AUTHOR]

Alkyl- and aryl vinyl sulfones were obtained by eosin Y (EY)-mediated visible-light photooxidation of sulfinate salts and the reaction of the resulting S-centered radicals with alkenes. Optimized reaction conditions, the sulfinate and alkene scope, and X-ray structural analyses of several reaction products are provided. A detailed spectroscopic study explains the reaction mechanism, which proceeds through the EY radical cation as key intermediate oxidizing the sulfinate salts. [ABSTRACT FROM AUTHOR]

Tetrahydrochromeno is a structural variant of spiropyran that undergoes a reversible ring-opening to generate a colored nitrophenolate . Earlier work confirmed this through trimethylsilyl cyanide trapping under continuous irradiation. We have performed transient absorption spectroscopy to further characterize the mechanism of the ring-opening reaction. Excitation at 355 nm produced a transient species with an absorption maximum at 445 nm, which we assign to the nitrophenolate unit of the ring-opened product. The transient absorption decays after ~970 ns with small optical density changes corresponding to a 0.15 quantum yield. Exposure to oxygen did not exhibit a significant deleterious effect on the photoisomerization of the chromeno dye. Time-dependent density functional theory corroborated spectroscopic assignments of the starting chromeno and the putative ring-opened . The excited state behavior of this system parallels the structurally similar oxazine system reported by Raymo and coworkers. The one significant difference is the longer lifetime of the photochemically generated from chromeno. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Here a systematic investigation on a regular type of porphyrin with outlying ruthenium groups, ({H 2 TPyP[Ru(terpy)(PPh 3 ) 2 ] 4 }8PF 6 ), and the isolated ruthenium substituent ([RuCl(terpy)(PPh 3 ) 2 ]PF 6 ) is reported. Steady state as well as time-resolved fluorescence and absorbance were employed in association with cyclic voltammetry. The steady state spectroscopy data suggest that the outlying ruthenium groups mostly interact with the second excited singlet state orbitals of the porphyrin ring, while the lowest singlet excited state electronic properties are weakly perturbed. Moreover, attachment of peripheral groups highly suggests the appearance of additional vibrational modes in the molecule, which leads to new internal conversion decay pathways that quenches both the radiative deactivation and the intersystem crossing to form the porphyrin triplet excited states. Transient absorption and electrochemical data reveal the absence of charge transfer between the porphyrin ring and ruthenium moieties. Energy transfer to the porphyrin ring is possible but not enough to efficiently quench the excited state of the ruthenium sites. Finally, our results shine light about future molecular engineering strategies that can be employed with the aim to obtain efficient light harvesting tetraruthenated porphyrin molecules. [ABSTRACT FROM AUTHOR]

Time-resolved spectroscopy is a powerful tool for studying fundamental photophysics in optoelectronic materials on a molecular temporal scale. In this review, we describe transient spectroscopic studies on fundamental photovoltaic conversion processes in polymer solar cells, which consist of a series of conversion processes such as photon absorption, exciton diffusion into a donor/acceptor interface, charge transfer at the interface, charge dissociation into free charge carriers, and charge collection to each electrode. These conversion processes are ultrafast phenomena and are ranging over the wide temporal scale from femtoseconds to microseconds, which can be directly observed by transient spectroscopy. [ABSTRACT FROM PUBLISHER]

Cytochrome c of Heliobacterium modesticaldum is the donor to P, the primary electron donor of the heliobacterial reaction center (HbRC). It is a membrane-anchored 14-kDa cytochrome that accomplishes electron transfer from the cytochrome bc complex to the HbRC. The petJ gene encoding cyt c was cloned and expressed in Escherichia coli with a hexahistidine tag replacing the lipid attachment site to create a soluble donor that could be made in a preparative scale. The recombinant cytochrome had spectral characteristics typical of a c-type cytochrome, including an asymmetric α-band, and a slightly red-shifted Soret band when reduced. The EPR spectrum of the oxidized protein was characteristic of a low-spin cytochrome. The midpoint potential of the recombinant cytochrome was +217 ± 10 mV. The interaction between soluble recombinant cytochrome c and the HbRC was also studied. Re-reduction of photooxidized P was accelerated by addition of reduced cytochrome c. The kinetics were characteristic of a bimolecular reaction with a second order rate of 1.53 × 10 M s at room temperature. The rate manifested a steep temperature dependence, with a calculated activation energy of 91 kJ mol, similar to that of the native protein in Heliobacillus gestii cells. These data demonstrate that the recombinant soluble cytochrome is comparable to the native protein, and likely lacks a discrete electrostatic binding site on the HbRC. [ABSTRACT FROM AUTHOR]

Abstract: Bipyridine bearing π-delocalized dithienypyrrole moieties (DTP) have been involved as ligands (L) in the preparation of RuL2(dcbpy)2+ and RuL(dcbpy)(NCS)2 dyes. These dyes exhibited wide absorption domains in solution and when adsorbed on TiO2 photoanodes, light harvesting was found to be excellent (absorbance>1 in the 350–600 nm range). Careful investigations, combining transient spectroscopy and ab initio computations evidenced the capture of the photoexcited electron by low lying orbitals centred on the DTP moiety thus limiting the efficiency in DSSC despite favourable redox potentials for both injection and ground state regeneration. [Copyright &y& Elsevier]

Periodic modulations that appear in the low-temperature transient reflectivity signal of a / single quantum well is studied. Similar anomalous oscillations are also reported in layered manganite [K. Kouyama et al., J. Phys. Soc. Jpn. 76 (2007) 123702(1-3).] We show that such periodic modulations are caused by changes in the linear reflectivity of the sample during transient reflectivity measurements. Studies carried out on reflectivity of different materials under identical conditions show that these modulations on the true transient reflectivity signal are caused by condensation of residual gases on the surface of quantum well. Methods to obtain reliable transient reflectivity data are also described. [ABSTRACT FROM AUTHOR]

The rate of bacterial photoinactivation in plasma by methylene blue (MB), especially for Gram-negative bacteria, has been reported to be lower, by about an order of magnitude, than the rate of inactivation in PBS and water solutions. This low inactivation rate we attribute to the bleaching of the 660-nm absorption band of MB in plasma that results in low yields of MB triplet states and consequently low singlet oxygen generation. We have recorded the change of the MB 660-nm-band optical density in plasma, albumin, and cysteine solutions, as a function of time, after 661-nm excitation. The transient triplet spectra were recorded and the singlet oxygen generated in these solutions was determined by the rate of decrease in the intensity of the 399-nm absorption band of 9, 10-anthracene dipropionic acid. We attribute the bleaching of MB, low singlet oxygen yield, and consequently the low inactivation rate of bacteria in plasma to the attachment of a hydrogen atom, from the S–H group of cysteine, to the central nitrogen atom of MB and formation of cysteine dimer. [ABSTRACT FROM AUTHOR]

We demonstrate long-lived rotational orientation of CO2 molecules originally prepared in an optical centrifuge. The optical centrifuge traps molecules in a strong optical field and spins them to high rotational states by angular acceleration of the optical field. In the case of CO2, the optical centrifuge creates ultra-high rotational states with J > 220. Polarisation-dependent, high-resolution transient infrared (IR) absorption was used to measure the spatial orientation of CO2 molecules in the (00°0, J= 76) state following the optical centrifuge pulse and subsequent collisional energy transfer. Transient Doppler-broadened line profiles show that C02 molecules in J = 76 probed with an IR transition dipole parallel to the initial plane of rotation are more plentiful and have higher translational temperatures than molecules with an IR transition dipole perpendicular to this plane. Time-dependent data show that the initial angular momentum orientation persists even after thousands of collisions, indicating that molecules in an optical centrifuge behave as quantum gyroscopes. These observations demonstrate that the optical centrifuge prepares an anisotropic rotational distribution and that molecules in oriented, ultra-high angular momentum states require many more collisions to randomise their orientation than do those in low rotational states. [ABSTRACT FROM AUTHOR]

We demonstrate long-lived rotational orientation of CO2 molecules originally prepared in an optical centrifuge. The optical centrifuge traps molecules in a strong optical field and spins them to high rotational states by angular acceleration of the optical field. In the case of CO2, the optical centrifuge creates ultra-high rotational states with J > 220. Polarisation-dependent, high-resolution transient infrared (IR) absorption was used to measure the spatial orientation of CO2 molecules in the (00°0, J= 76) state following the optical centrifuge pulse and subsequent collisional energy transfer. Transient Doppler-broadened line profiles show that C02 molecules in J = 76 probed with an IR transition dipole parallel to the initial plane of rotation are more plentiful and have higher translational temperatures than molecules with an IR transition dipole perpendicular to this plane. Time-dependent data show that the initial angular momentum orientation persists even after thousands of collisions, indicating that molecules in an optical centrifuge behave as quantum gyroscopes. These observations demonstrate that the optical centrifuge prepares an anisotropic rotational distribution and that molecules in oriented, ultra-high angular momentum states require many more collisions to randomise their orientation than do those in low rotational states. [ABSTRACT FROM AUTHOR]

We measured the picoseconds (ps) transient dynamics of photoexcitations in blends of regio-regular poly(3-hexyl-thiophene) (RR-P3HT) (donors-D) and fullerene (PCBM) (acceptor-A) in an unprecedented broad spectral range of 0.25 to 2.5 eV. In D-A blends with maximum domain separation, such as RR-P3HT/PCBM, with (1.2:1) weight ratio having solar cell power conversion efficiency of ~4%, we found that although the intrachain excitons in the polymer domains decay within ~10 ps, no charge polarons are generated at their expense up to ~1 ns. Instead, there is a build-up of charge-transfer (CT) excitons at the D-A interfaces having the same kinetics as the exciton decay. The CT excitons dissociate into separate polarons in the D and A domains at a later time (>1 ns). This "two-step" charge photogeneration process may be typical in organic bulk heterojunction cells. We also report the effect of adding spin 1/2 radicals, Galvinoxyl on the ultrafast photoexcitation dynamics in annealed films of RR-P3HT/PCBM blend. The addition of Galvinoxyl radicals to the blend reduces the geminate recombination rate of photogenerated CT excitons. In addition, the photoexcitation dynamics in a new D-A blend of RR-P3HT/Indene C60 trisadduct (ICTA) has been studied and compared with the dynamics in RR-P3HT/PCBM. [ABSTRACT FROM AUTHOR]

Abstract: We present recent developments in the synthesis and in the functional study of non covalently bound porphyrin/carbon nanotube compounds. The issue of the chemical stability of non covalent compounds is tackled by means of micelle assisted chemistry. The non covalent functionalization allows to preserve the electronic integrity of the nanotubes that display bright NIR luminescence. In the same time, the coupling between the subunits is very strong and leads to efficient energy transfer and PL quenching of the chromophore. This transfer occurs on a subpicosecond time-scale and leads to a near 100% efficiency. It allows to uniformly excite a whole set of chiral species with a single wavelength excitation. Insight into the transfer mechanism is gained by means of transient absorption spectroscopy. [Copyright &y& Elsevier]

Abstract: Transient absorption measurement of urea-anthracene species nPUA (n =1, 2, 9; PUA=1-anthracen-n-yl-3-phenylurea) in the presence of acetate anions (tetrabutylammonium acetate, TBAAc) gave relatively long-lived transient species with lifetimes of ∼100μs, which were unaffected by O2. The lifetimes showed significant temperature dependence, which allowed us to determine ΔH ‡ and ΔS ‡. ΔS ‡ had a large negative value, in contrast to ΔH ‡, indicating that the dissipation process of the transient species was entropy-controlled. A linear relationship between TΔS ‡ and ΔH ‡ suggested entropy–enthalpy compensation, which is generally found in host–guest systems with hydrogen bonding. These findings allowed us to assign the transient species as X, which is the ground state responsible for longer wavelength emissions, and conclude that the dissipation of the transient species corresponded to recovery of the complex in the ground state. We propose a reaction scheme for the photochemical process applying to urea derivatives in the presence of anions. [Copyright &y& Elsevier]

Abstract: This review considers transient spectroscopic studies of electron transfer reactions between nucleic acids and the excited states of transition metal complexes containing dipyridophenazine or related ligands and focuses mainly on complexes of ruthenium, chromium and rhenium. Particular emphasis is placed on systems where transient UV/visible and/or infrared absorption spectroscopy have been employed. [Copyright &y& Elsevier]

Abstract: The photochromic reaction dynamics of spiroindolinenaphthoxazine and its 6′CN and 5′CHO substituted compounds is investigated in different solvents by femtosecond transient absorption spectroscopy. In addition to the formation of the merocyanine coloured form (ring-opened trans form, OF), another short-lived intermediate species is produced upon photoexcitation, which is not a precursor to the OF product but which is formed in parallel to it via a competing relaxation process. This species is ascribable to either a relaxed s-cis ring-opened isomer on the ground state potential energy surface or to a metastable minimum of the excited S1 state potential energy surface of the ring-closed form. The observed kinetics suggest that the production of OF (photocoloraton reaction) is controlled by the efficiency of the competing process rather than by an s-cis – trans isomerisation energy barrier. [ABSTRACT FROM AUTHOR]