ACS Physical Chemistry Au最新文献

Photoisomerization, the structural alteration of molecules upon absorption of light, is crucial for the function of biological chromophores such as retinal in opsins, proteins vital for vision and other light-sensitive processes. The intrinsic selectivity of this isomerization process (i.e., which double bond in the chromophore is isomerized) is governed by both the inherent properties of the chromophore and its surrounding environment. In this study, we employ the extended multistate complete active space second-order perturbation theory (XMS-CASPT2) method to investigate photoisomerization selectivity in linear conjugated chromophores, focusing on two simple molecular models resembling retinal. By analyzing electronic energies, intramolecular charge separation, and conical intersection topographies in the gas phase, we show that the photoproduct formed by rotation around the double bond near the Schiff base is energetically favored. The topographic differences at the conical intersections leading to different photoproducts reveal differences in photodynamics. In multiphoton excitation, the primary photoproduct typically reverts to the initial configuration rather than rotating around a different double bond. Our study offers new insights into the photodynamics of photoisomerizing double bonds in π-conjugated chromophores. We anticipate that our findings will provide valuable perspectives for advancing the understanding of biological chromophores and for designing efficient photochemical switches with applications in molecular electronics and phototherapy.

Photoisomerization, the structural alteration of molecules upon absorption of light, is crucial for the function of biological chromophores such as retinal in opsins, proteins vital for vision and other light-sensitive processes. The intrinsic selectivity of this isomerization process (i.e., which double bond in the chromophore is isomerized) is governed by both the inherent properties of the chromophore and its surrounding environment. In this study, we employ the extended multistate complete active space second-order perturbation theory (XMS-CASPT2) method to investigate photoisomerization selectivity in linear conjugated chromophores, focusing on two simple molecular models resembling retinal. By analyzing electronic energies, intramolecular charge separation, and conical intersection topographies in the gas phase, we show that the photoproduct formed by rotation around the double bond near the Schiff base is energetically favored. The topographic differences at the conical intersections leading to different photoproducts reveal differences in photodynamics. In multiphoton excitation, the primary photoproduct typically reverts to the initial configuration rather than rotating around a different double bond. Our study offers new insights into the photodynamics of photoisomerizing double bonds in π-conjugated chromophores. We anticipate that our findings will provide valuable perspectives for advancing the understanding of biological chromophores and for designing efficient photochemical switches with applications in molecular electronics and phototherapy.

Efficient photoredox chemical transformations are essential to the development of novel, cost-effective, and environmentally friendly synthetic methodologies. The concept of the entatic state in bioinorganic catalysis proposes that a preorganized structural configuration can reduce the energy barriers associated with chemical reactions. This concept provides one of the guiding principles to enhance catalytic efficiency by maintaining high-energy conformations close to the reaction's transition state. Copper(I)-based photocatalysts, recognized for their low toxicity and highly negative oxidation potentials, are of particular interest in entasis studies. In this study, we explore the impact of entasis caused by stress induced by the surrounding lattice on the excited state dynamics of a prototypical copper(I)-based photocatalyst in a single crystal form. Using femtosecond broadband transient absorption spectroscopy, we show that triplet state formation from the entactic state is faster (∼3.9 ps) in crystals compared with solution (∼11.3 ps). The observed faster intersystem crossing in crystals hints toward the possible existence of distorted square planar geometry with higher spin-orbit coupling at the minima of the S₁ state. We further discuss the influence of entasis on vibrationally coherent photoinduced Jahn-Teller distortions. Our findings reveal the photophysical properties of the copper complex under lattice-induced stress, which can be extended to enhance the broader applicability of the entatic state concept in other transition metal systems. Understanding how environmental stress-induced geometric constraints within crystal lattices affect photochemical behavior opens avenues for designing more efficient photocatalytic systems based on transition metals, potentially enhancing their applicability to sustainable chemical synthesis.

Efficient photoredox chemical transformations are essential to the development of novel, cost-effective, and environmentally friendly synthetic methodologies. The concept of the entatic state in bioinorganic catalysis proposes that a preorganized structural configuration can reduce the energy barriers associated with chemical reactions. This concept provides one of the guiding principles to enhance catalytic efficiency by maintaining high-energy conformations close to the reaction’s transition state. Copper(I)-based photocatalysts, recognized for their low toxicity and highly negative oxidation potentials, are of particular interest in entasis studies. In this study, we explore the impact of entasis caused by stress induced by the surrounding lattice on the excited state dynamics of a prototypical copper(I)-based photocatalyst in a single crystal form. Using femtosecond broadband transient absorption spectroscopy, we show that triplet state formation from the entactic state is faster (∼3.9 ps) in crystals compared with solution (∼11.3 ps). The observed faster intersystem crossing in crystals hints toward the possible existence of distorted square planar geometry with higher spin–orbit coupling at the minima of the S₁ state. We further discuss the influence of entasis on vibrationally coherent photoinduced Jahn–Teller distortions. Our findings reveal the photophysical properties of the copper complex under lattice-induced stress, which can be extended to enhance the broader applicability of the entatic state concept in other transition metal systems. Understanding how environmental stress-induced geometric constraints within crystal lattices affect photochemical behavior opens avenues for designing more efficient photocatalytic systems based on transition metals, potentially enhancing their applicability to sustainable chemical synthesis.

Roundabout (RA) is an important indirect mechanism for gas-phase X^– + CH₃Y → XCH₃ + Y^– S_N2 reactions at a high collision energy. It refers to the rotation of the CH₃-group by half or multiple circles upon the collision of incoming nucleophiles before substitution takes place. The RA mechanism was first discovered in the Cl^– + CH₃I S_N2 reaction to explain the energy transfer observed in crossed molecular beam imaging experiments in 2008. Since then, the RA mechanism and its variants have been observed not only in multiple C-centered S_N2 reactions, but also in N-centered S_N2 reactions, proton transfer reactions, and elimination reactions. This work reviewed recent studies on the RA mechanism and summarized the characteristics of RA mechanisms in terms of variant types, product energy partitioning, and product velocity scattering angle distribution. RA mechanisms usually happen at small impact parameters and tend to couple with other mechanisms at relatively low collision energy, and the available energy of roundabout trajectories is primarily partitioned to internal energy. Factors that affect the importance of the RA mechanism were analyzed, including the type of leaving group and nucleophile, collision energy, and microsolvation. A massive leaving group and relatively high collision energy are prerequisite for the occurrence of the roundabout mechanism. Interestingly, when reacting with CH₃I, the importance of RA mechanisms follows an order of Cl^– > HO^– > F^–, and such a nucleophile dependence was attributed to the difference in proton affinity and size of the nucleophile.

Spin relaxation of charge carriers in strongly quantum confined perovskite magic-sized clusters has been probed, for the first time, by using polarization-controlled femtosecond transient absorption (fs-TA) spectroscopy. Fs-TA measurements with a circularly polarized pump and probe allowed for the determination of the exciton spin relaxation lifetime (∼1.5 ps) at room temperature based on the dynamics of a photoinduced absorption (PIA) feature peaked at 458 nm. This spin lifetime is shorter than that of perovskite quantum dots (PQDs) with a larger size, and the results suggest that exciton confinement and defects likely play a more important role in these strongly quantum confined magic-sized clusters with a larger surface-to-volume ratio.

While exploring the behavior of lysozyme powders at different percentages of rehydration by differential scanning calorimetry, we noticed a small peak persistently on the left of the melting point of bulk water, which, when heating up the system, was always around −10 °C. The intensity of the transition was maximal at 160% rehydration and disappeared at higher values. By comparing the premelting peak properties in H₂O and D₂O, we attributed it to freezable water bound on the protein surface. This is the first time that such an observation has been reported.