Modulating Electron Transfer in an Organic Reaction via Chemical Group Modification of the Photocatalyst

Exploring the Franck-Condon region of a photoexcited charge transfer complex in solution to interpret femtosecond stimulated Raman spectroscopy: excited state electronic structure methods to unveil non-radiative pathways

We present electronic structure methods to unveil the non-radiative pathways of photoinduced charge transfer (CT) reactions that play a main role in photophysics and light harvesting technologies. A prototypical π-stacked molecular complex consisting of an electron donor (1-chloronaphthalene, 1ClN) and an electron acceptor (tetracyanoethylene, TCNE) was investigated in dichloromethane solution for this purpose. The characterization of TCNE:π:1ClN in both its equilibrium ground and photoinduced low-lying CT electronic states was performed by using a reliable and accurate theoretical-computational methodology exploiting ab initio molecular dynamics simulations. The structural and vibrational time evolution of key vibrational modes is found to be in excellent agreement with femtosecond stimulated Raman spectroscopy experiments [R. A. Mathies et al., J. Phys. Chem. A, 2018, 122, 14, 3594], unveiling a correlation between vibrational fingerprints and electronic properties. The evaluation of nonadiabatic coupling matrix elements along generalized normal modes has made possible the interpretation on the molecular scale of the activation of nonradiative relaxation pathways towards the ground electronic state. In particular, two low frequency vibrational modes such as the out of plane bending and dimer breathing and the TCNE central C[double bond, length as m-dash]C stretching play a prominent role in relaxation phenomena from the electronic CT state to the ground state one.

Adsorption-photocatalysis synergistic removal of contaminants under antibiotic and Cr(VI) coexistence environment using non-metal g-C3N4 based nanomaterial obtained by supramolecular self-assembly method

Due to the rapid development of modern industry, the coexistence of antibiotics and inorganic heavy metals pollutants in wastewater has become a universal phenomenon. Therefore, developing efficient and eco-friendly photocatalyst for mixed pollutants degradation is significant. In this work, a well-designed phosphorus and sulfur co-doped g-C₃N₄ with feeble N vacancies catalyst (P/S-g-C₃N_x) was fabricated by supramolecular self-assembly method, and was applied to remove berberine hydrochloride (BH) and Cr(VI) simultaneously with the synergy of adsorption-photocatalysis. A series of experiments was conducted to unveil the synergistic mechanism. The kinetic models indicated that the adsorption of P/S-g-C₃N_x improved the BH removal process by accelerating the photo-degradation, because the adsorption rate > surface degradation rate > bulk degradation rate. Besides, the photo-degradation process improved the BH removal rate by regenerating the adsorption sites of P/S-g-C₃N_x. Moreover, from the experiments in BH-Cr(VI) mixed solution system, the existence of BH also enhanced the surface adsorption of Cr(VI) in P/S-g-C₃N_x sample, and the reduction rate of Cr(VI) was also promoted with the existence of BH. Overall, the results of this investigation suggest that the adsorption-photocatalysis synergy method is an efficient way to eliminate organic pollutant and Cr(VI) simultaneously.

Computational Analysis of Electron Transfer Kinetics for CO2 Reduction with Organic Photoredox Catalysts

We present a fundamental description of the electron transfer (ET) step from substituted oligo(p-phenylene) (OPP) radical anions to CO₂, with the larger goal of assessing the viability of underexplored, organic photoredox routes for utilization of anthropogenic CO₂. This work varies the electrophilicity of para-substituents to OPP and probes the dependence of rate coefficients and interfragment interactions on the substituent Hammett parameter, σ_p, using constrained density functional theory (CDFT) and energy decomposition analysis (EDA). Large electronic couplings across substituents indicates an adiabatic electron transfer process for reactants at contact. As one might intuitively expect, free energy changes dominate trends in ET rate coefficients in most cases, and rates increase with substituent electron-donating ability. However, we observe an unexpected dip in rate coefficients for the most electron-donating groups, due to the combined impact of flattening free energies and a steep increase in reorganization energies. Our analysis shows that, with decreasing σ_p, flattening OPP LUMO levels lower the marginal increase in free energy. EDA reveals trends in electrostatics and charge transfer interactions between the catalyst and substrate fragments that influence free energy changes across substituents. Reorganization energies do not exhibit a direct dependence on σ_p and are largely similar across systems, with the exception of substituents containing lone pairs of electrons that exhibit significant deformation upon electron transfer. Our study therefore suggests that while a wide range of ET rates are observed, there is an upper limit to rate enhancements achievable by only tuning the substituent electrophilicity.