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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]

Accurate tuning of the electronic and photophysical properties of quantum dots is required to maximize the light conversion efficiencies in semiconductor-assisted processes. Herein, we report a facile synthetic procedure for AgIn(S x Se 1- x ) 2 quantum dots with S content ( x ) ranging from 1 to 0. This simple approach allowed us to tune the bandgap (2.6-1.9 eV) and extend the absorption of AgIn(S x Se 1- x ) 2 quantum dots to lower photon energies (near-IR) while maintaining a small QD size (∼5 nm). Ultraviolet spectroscopy studies revealed that the change in the bandgap is modulated by the electronic shifts in both the valence band and the conduction band positions. The negative overall charge of the as-synthesized quantum dots enabled us to make films of quantum dots on mesoscopic TiO 2 . Excited state studies of the AgIn(S x Se 1- x ) 2 quantum dot films demonstrated a fast charge injection to TiO 2 , and the electron transfer rate constant was found to be 1.5-3.5 × 10 11 s -1 . The results of this work present AgIn(S x Se 1- x ) 2 quantum dots synthesized by the one-step method as a potential candidate for designing light-harvesting assemblies.

For the efficient photocatalytic oxidation of organic pollutants at surfaces of semiconductors, photogenerated holes shall be separated toward the surface and transferred to reactive surface sites, whereas the transfer of photogenerated electrons toward the surface shall be minimized. In this Research Article, the identification of suitable synthesis control of charge separation combined with an in-depth understanding of charge kinetics and trapping passivation mechanisms at the related surfaces can provide tremendous opportunities for boosting the photocatalytic performance. In this work, a comprehensive transient surface photovoltage spectroscopy study of charge separation at anatase TiO 2 thin films, synthesized by ultrasonic spray pyrolysis from titanium(IV) isopropoxide (TTIP)-acetylacetone (AcacH) based precursor is reported. By varying the amount of AcacH in the precursor solution, an experimental approach of synthesis control of the charge transfer toward TiO 2 surface is provided for the first time. An increased amount of AcacH in the precursor promotes transition from preferential fast electron to preferential fast hole transfer toward anatase surface, correlating with a strong increase of the photocatalytic decomposition rate of organic pollutants. Suitable mechanisms of AcacH-induced passivation of electron traps at TiO 2 surfaces are analyzed, providing a new degree of freedom for tailoring the properties of photocatalytic systems.