Modeling organic reactivity and photophysical processes: DFT applications of aza-heterocyclic compounds and organic sensitizers

Abstract

This study is composed of two main components, involving Density Functional Theory investigations in terms of small organic reactions and organic dye-semiconductor systems. In the first part, ring-expansion reactions of 1-azoniabicyclo[n.1.0]alkanes have been modeled to endeavor the mechanistic aspects of two competitive pathways. Sev eral nucleophiles and their regioselectivity are scrutinized in terms of different level of theories and solvation methods. As starting bicyclic structures, 1-azoniabicyclo[3.1.0] hexane and 1-azoniabicyclo[4.1.0]heptane ions have been used, while the computational work of the latter has been done the first time in the literature. In the second part, the aim of the study was to probe the effective modeling of isolated sensitizers and dye@semiconductor interfaces in Dye-sensitized Solar Cells (DSSCs). Density functional theory (DFT) and Time-Dependent Density functional theory (TDDFT) calculations have been performed to elucidate the absorption and charge transfer in sensitizers and dye-to-semiconductor electron injection process. Den sity of states (DOS) have been analyzed by means of two main approaches: i) single dye@SC model, ii) dye@SC model with periodic boundary conditions. In addition to periodicity, effects of solvation, inclusion of non-covalent interactions and different DFT functionals have been tested within the framework of organic dyes.