Synthesis and properties of perylene-bridge-anchor chromophoric compounds
Creators: name: Harmer, Ryan
Publisher: name: No Publisher Supplied
Year: 2022

description: Photoinduced electron transfer between a light-absorbing molecule and a metal oxide semiconductor remains at the center of intense research because of the numerous potential applications in solar energy conversion. Perylene-bridge-anchor compounds are excellent models for studying important fundamental aspects of charge transfer processes on TiO2, one of the most commonly investigated semiconductors used for this purpose, because of their favorable photophysical properties. Despite their usefulness, advances are still needed to fully exploit synthetically the rich substitution pattern of the perylene core. The main hypothesis of this thesis is that the peri, ortho, and bay positions on perylene differ in electronic structure and reactivity, and that these differences can be used to tune interfacial charge transfer dynamics. In this thesis we describe the synthesis and properties of novel 2,5-di-tert-butylperylene-bridge-anchor compounds with either one or two linkers (linker = bridge-anchor) in peri and ortho positions. To synthesize them we utilized a combination of Friedel-Crafts alkylations, bromination, iridium-catalyzed borylation, and palladium-catalyzed cross-coupling reactions. Photophysical characterization and computational analysis by density functional theory (DFT) and time-dependent DFT (TD-DFT) were carried out on a family of perylene derivatives functionalized with one or two acrylic or propionic acid linkers in peri and ortho positions. The same family of perylene-bridge-anchor compounds were bound to TiO2 and characterized by UV-Vis absorption spectra. The linker effect on the photophysical properties of the perylene core were investigated by modifying the conjugation (acrylic or propionic acid), substitution position (peri or ortho), and/or number (one or two) of the linkers on the perylene framework, and the experimental results rationalized by frontier orbital analysis. The conjugated linkers in the peri position show the largest amount of delocalization of the lowest unoccupied molecular orbital (LUMO) of the perylene core onto the linker, thus these compounds showed the largest red shift of the absorption and emission spectra. Conversely, linkers in the ortho positions weakly affect the frontier orbitals of the perylene core and did not significantly affect the photophysical properties. The saturated linkers in either the peri or ortho positions, did not affect the frontier orbitals, or photophysical properties of perylene. Finally, the one and two linker, peri and ortho acrylic acids were used to probe the conformational and binding effects on interfacial electron transfer (IET) to TiO2 by the Gundlach group from the University of Delaware and the Rego group from the Universidade Federal de Santa Catarina (UFSC) in Brazil. The bis peri acrylic acid, surprisingly, showed significantly slower IET, which theory suggests is due to small conformational changes arising from the steric interaction between linkers. This study opens up new avenues for investigations, that can utilize chemically different linkers with varied binding strengths and functions, to improve fundamental understanding of IET.