Photophysical Studies of Conjugated Chromophores on Peptide Templates

University Of Rochester, Rochester NY

Investigators

Abstract

Technical: This project aims to address basic questions that arise in connection with the solid-state photophysics of conjugated polymers and oligomers, which are of broad interest in optoelectronic device applications. The questions are: Why is the photoluminescence (PL) quantum yield in conjugated polymer films so much lower than in solution even though the excited lifetimes are at least as long in the films? What fraction of paired charges with uncorrelated spins on adjacent conjugation segments will recombine to form singlet excited states and how does this depend on morphology? Do energy transfer and formation of interchromophore states following photoexcitation compete with charge transfer in donor/acceptor systems typical of organic photovoltaics? During the project, Kristi Kiick's group at the University of Delaware will synthesize rigid peptides as scaffolds where conjugated oligomers can be placed at specific places on the peptide through reactions with judiciously placed non-natural amino acids. Lewis Rothberg's group at the University of Rochester will perform steady-state and transient spectroscopy to measure how the altering the relative positions and orientations of the chromophores changes the photophysics. By changing the distance between two identical oligomers on a peptide scaffold, it is possible to simulate the photophysical behavior of conjugated polymers as they go from dilute solution to films. The project is designed to measure singlet-triplet branching in charge recombination that is a limiting factor in fluorescent organic light-emitting diode technology, to determine whether and when energy transfer can compete with charge transfer and what the consequences are for efficiency of photoinduced charge separation, and to find out whether photogeneration of interchromophore species can suppress charge generation in donor/acceptor systems characteristic of organic photovoltaics. Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance, and is expected to provide prescriptive information on how chromophores would be best organized for electroluminescent device applications. This project provides student training in a highly collaborative and interdisciplinary environment, including organic synthesis, materials characterization, and laser spectroscopy. Involving students in closely coordinated collaborative research is an important part of their training and especially valuable in materials science.