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[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]

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]

• 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]

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]

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]

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]

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]

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]

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]

Abstract: Photon upconversion, the process wherein light of long wavelength is frequency converted to photons of higher energy, is readily achieved at low incident power through sensitized triplet–triplet annihilation (TTA) in various chromophore combinations spanning the UV to the near-IR. This emerging wavelength-shifting technology truly represents a viable route towards converting low energy terrestrial solar photons into light adequate to drive electron transfer in operational photovoltaics. Generalized molecular design constraints, all operational examples reported to date, and measurement techniques applied to these low power nonlinear processes are reviewed in this contribution. In many instances, direct visualization of this phenomenon is presented in solution and within various polymeric host materials. [ABSTRACT FROM AUTHOR]

Abstract: The excited-state intramolecular proton transfer in the aromatic polycycle 10-hydroxybenzo[h]quinoline is investigated by means of transient absorption experiments with 30fs time resolution, classical dynamics and wavepacket dynamics. The experiments establish the ultrafast transfer after UV excitation and show signatures of coherent vibrational motion in the keto product. To elucidate details of the proton transfer mechanism, the classical dynamics is also performed for 2-(2′-hydroxyphenyl)benzothiazole and the results are compared. For both systems the proton transfer takes place on the ultrafast scale of 30–40fs, with good agreement between the theoretical investigations and the measurements. The dynamics simulations show that for both molecules the proton is handed over by means of skeletal deformation of the molecule. Due to the more rigid structure of 10-hydroxybenzo[h]quinoline the hydrogen migration mode participates more actively than in 2-(2′-hydroxyphenyl)benzothiazole. [Copyright &y& Elsevier]

Abstract: Understanding the thermodynamics of ligand binding in metallo-proteins is of critical importance in probing the underlying energetic basis for the reaction mechanism. However, many kinetic events occurring subsequent to ligand binding/release are on a time scale outside of that accessible using traditional calorimetric techniques thus making the construction of thermodynamic profiles for early kinetic events difficult. Photothermal methods have enjoyed considerable success in probing photo-triggered reactions on timescales ranging from ∼ns to >ms. These techniques, including photoacoustic calorimetry (PAC) and photothermal beam deflection (PBD), have been applied to obtain both molar volume and enthalpy changes for a wide range of biological processes including ligand binding to metallo-proteins. Here we review the progress made to date in utilizing photothermal methods (PAC and PBD) to probe the thermodynamics of small molecule binding to heme proteins ranging from simple globin-type proteins to the more complex heme/copper oxidases. [Copyright &y& Elsevier]

The photophysical properties of mononuclear PtII chromophores of the general structural formulae: Pt(LL)(C≡CR)2 and [Pt(LLL)(C≡CR)]+ (LL = substituted or unsubstituted 2,2′-bipyridine; LLL = substituted or unsubstituted 2,2′:6′,2″-terpyridine; R = aryl or alkyl) are described. Topics related to their preparation, spectroscopy, photochemistry, and photophysics are reviewed. [Copyright &y& Elsevier]

Our recent experimental and theoretical work on the kinetics and mechanism of electron injection and charge recombination in dye-sensitized nanocrystalline semiconductors is reviewed. In our experimental studies of electron injection, nanocrystalline ZnO films were chosen as the semiconductor. In order to reveal the kinetics and mechanism of electron injection we have developed several types of transient absorption spectrometers which enable us to observe the time profiles of the absorption spectra of the oxidized form of dyes and conducting electrons with high sensitivity over a wavelength range from near IR to visible and over a time range from femtoseconds to submicroseconds. For N3 dye/ZnO system, the aggregation of N3 dyes and its effect on electron injection have been clarified spectroscopically. The electron injection process has been measured by a femtosecond pump-probe method and it has been found that a fraction of electron injection occurs via an intermediate state. The absolute efficiency of electron injection has been measured and a new theoretical model has been developed for electron injection to explain the dependence of the efficiency of electron injection on the free energy change for injection. Concerning charge recombination a consistent theoretical model has been developed which explains not only the observed highly dispersive kinetics of charge recombination but also the effects of the light intensity, the applied bias and the dye structure on the kinetics. [Copyright &y& Elsevier]

The degradation of a prototypical halogenoaromatic pollutant, 4-chloroaniline (4-CA), photoinduced by Fe(III) species, has been studied in acidic aqueous solutions (pH 2–4) of Fe(ClO4)3 by means of product analysis and nanosecond transient absorption spectroscopy. The degradation process is initiated by the attack of OH radicals on 4-CA, leading to radical cations, 4-CA⋅+ as the major transient species. At high photon fluences, the decay of 4-CA⋅+ is dominated by second-order reactions; an accelerating effect of Fe(III) could be evidenced at low fluence. A large number of minor reaction intermediates could be detected by product analysis following continuous irradiation at λexc=365 nm of aerated solutions, arising from ring substitution, ring opening and oligomerization processes. At higher concentration of 4-CA, the specificity of the degradation process increases; the oligomerization pathway becomes predominant and leads to three major oligomeric products, one of which could be unequivocally identified, while probable structures were proposed for the other two. The chemical nature of these products, as well as the observation of the p-benzoquinone/hydroquinone couple as the major photoproduct in deaerated solution, led to the proposal that p-benzoquinone monoimine is a key intermediate in the degradation of 4-CA. Direct oxidation of 4-CA⋅+ by Fe(III) is put forward as a possible explanation for its formation. Prolonged irradiation at λexc=365 nm in the presence of oxygen leads to complete mineralization; the process is, however, complex due to the formation of light-absorbing aromatic intermediates on the one hand, and to the behavior of the Fe(III)/Fe(II) redox couple during irradiation on the other. Fe(III)-photoinduced oxidation of 4-CA is a fairly efficient process as long as the photoinducing Fe(III) species are not depleted. The further progress of the reaction requires the reoxidation of Fe(II) into Fe(III), which is accomplished in processes requiring both light and oxygen, probably by reactions of Fe(II) with photoinduced oxidizing radicals. [Copyright &y& Elsevier]

Abstract: The possibility to couple a transient electrochemical detection of the redox intermediates produced by a picosecond electron accelerator is explored. The principle is demonstrated with the well-behaved methylviologen radical cation that can be reoxidised at the electrode and simultaneously detected by transient absorption. [Copyright &y& Elsevier]

Metal oxide has a high energy bandgap and passes the visible light to enlighten the vision to human eyes. However, the strong and harmful UV light is easily captured by large bandgap metal oxide materials. One of the promising applications of metal oxide manipulation would be the transparent solar cells for the transparent window, to guarantee the view of visible light and generate electric power from the invisible UV radiation. Herein, we demonstrate the all-transparent photovoltaics for see-through applications with the functional deployment of TiO 2 layer. P-type NiO and n-type ZnO form a heterojunction to establish a photovoltage. TiO 2 layer with donor concentration >1019 cm−3 has flat-band potential of 0.4 V vs reversible hydrogen electrode (RHE) and is significantly higher than that of the photoactive ZnO layer, TiO 2 layer insertion enables the multifunctions of giving a back surface field and also serving as a carrier selective transport layer. The ultrathin TiO 2 embedded ZnO/NiO device has Ag nanowire top electrode and is highly transparent (>50%) in the visible range. This transparent solar cell provides power conversion efficiency of 6.1% and incident photon to charge carrier efficiency of 79.5% under UV light illumination. Mott-Schottky analysis showed the flat band potential to be 0.9 V by using the TiO 2 layer insertion to induce the significant higher photovoltage and photocurrent on/off ratio of higher than 5 × 105 and played a vital role in the enhanced performance of ZnO/NiO heterostructure. We demonstrated the enhancement of the minority carrier lifetime for a broadband of light illumination via back surface field formation and proposed the energy band-diagram. We may suggest that this high transparent photovoltaic device can be functionally applied on-demands of power generation windows of electronic devices, vehicles and buildings. Back surface field triggered all-transparent oxide photovoltaic device for broadband high-performance electric power window. An ultrathin TiO 2 insertion at the ZnO/FTO interface establishes the back surface field to induce efficient carrier collection. According to this feature, high-performing all transparent (>50% for visible range) solar cell was achieved by the power conversion efficiency of ∼6% under the UV (λ = 365 nm) light illumination. Image 1 • Transparent photovoltaic (TPV) device based on metal oxide heterojunctions. • TPV has high transparency (50>%) in the visible region. • TPV can be used for electric power window (EPW) for power generation. • EPW shows high V OC (0.7V) with a conversion efficiency of 6%. [ABSTRACT FROM AUTHOR]

The photophysics of a donor-acceptor system in which efficient electronic energy transfer occurs is analyzed and discussed by the combined use of steady-state and time-resolved spectroscopy and DFT/TD-DFT computations. The donor and acceptor units belong to the class of BODIPY chromophores, and are conveniently linked through a calixarene scaffold, which allows the control of the mutual orientation and distance between chromophores. Our results highlight that the energy transfer process occurs with multiexponential dynamics strongly influenced by the solvent. Although the conformation adopted by the system is very similar in all the analyzed solvents, highly polar media favour fast and efficient energy transfer. On the contrary, in non-polar media, the concomitant occurrence of backward energy transfer causes a significant slowdown of the process. The inverse of the energy transfer rates calculated at the TDDFT level are in very good agreement with the experimental kinetics measured with transient absorption spectroscopy. Image 1 • A BODIPY-decorated calix [4]arene is prepared as model system for energy transfer. • Steady-state spectroscopy reveals efficient energy transfer between the BODIPYs. • Transient absorption suggest that energy transfer is influenced by medium polarity. • Energy transfer rates are calculated at the TD-DFT level of theory. [ABSTRACT FROM AUTHOR]