Understanding the effects of building block rings of π electron-rich organic photocatalysts in CO2 transformation to amino acids.

Understanding the effective factors in the performance of some Oligo (p-phenylenes) (OPPs) and Polycyclic Aromatic Hydrocarbons (PAHs), as efficient organocatalysts in photocatalytic CO2 transformations are the main goals of this investigation. The studies are based on density functional theory (DFT) calculations on the mechanistic aspects of C-C bond formation through a coupling reaction between CO2•- and amine radical. The reaction is performed through two successive single electron transfer steps. After careful kinetic investigations by Marcus' theory rules, powerful descriptors are used to describe the behavior of observed barrier energies of electron transfer steps. The studied PAHs and OPPs consist of different numbers of rings. Thus, it can be considered different charge densities, afforded from π electrons, of PAHs and OPPs that cause distinguished efficiency in kinetic aspects of electron transfer steps. Electrostatic Surface Potential (ESP) analyses reveal a good relationship between the charge density of the studied organocatalysts in single electron transfer (SET) steps and the kinetic parameters of the steps. Moreover, the contribution of rings in the framework of PAHs and OPPs would be another effective factor in the barrier energies of SET steps. Aromatic properties of the rings, studied by the Anisotropy of the Current-Induced Density (ACID), Nucleus-Independent Chemical Shift (NICS), the multi-center bond order (MCBO), and AV1245 Indexes, are the other impressive factors in the role of rings in SET steps. The results show that the aromatic properties of the rings are not similar to each other. Higher aromaticity affords remarkable reluctance of the corresponding ring to participate in SET steps.

Solvent Effects on Intra-/Intermolecular Charge Transfer in Indoloquinoxaline-Based Dyes.

In this work, kinetics and dynamics of the functionality of indoloquinoxaline-based dye-sensitized solar cells (DSSCs), QX22-QX25, were investigated in gas and solvent media. Quantum chemistry properties of the dyes at the excited states show that each moiety of the (D)2-A-π-A system has a specific effect on the photovoltaic properties. Solvent effect analysis shows that among ethanol, toluene, tetrahydrofuran, and methylene dichloride, toluene is the preferred medium for intra-/intermolecular charge transfer, dynamically and kinetically. Moreover, the behavior of the light harvesting efficiency (LHE) and incident photon-to-current efficiency (IPCE) are not similar, due to a strong effect of the Gibbs energy of electron injection on the energy conversion efficiency. Finally, the dye composed of -COOH as the anchoring group and thiophene as the π-spacer is the best candidate to be applied in DSSC due to its better efficiency originated from a lower electrophilicity and electronic chemical potential.