Photophysics of Single-walled Carbon Nanotubes and Thin-film Conjugated Polymers Within π-electron Model

Abstract

Electron-electron interaction effects play important role in the photophysics of complex organic materials such as π-conjugated polymers and single-walled carbon nanotubes. Our theoretical work within a π-electron model captures the essential mechanism of the photophysics in these apparently different π-conjugated systems. In both polymer and nanotube systems, we not only explain existing experiments but also make testable predictions. In the area of π-conjugated polymers, we develop a theory of the electronic structure and photophysics of interacting chains to understand the differences between solutions and films. While photoexcitation generates only the optical exciton in solutions, the optical exciton as well as weakly allowed excimers are generated in films. Photoinduced absorption in films is primarily from the lowest excimer. We are also able to explain peculiarities associated with photoluminescence, including delayed photoluminescence and its quenching by electric field. We thereby resolve controversies in the field that are more than a decade old. In the area of single-walled carbon nanotubes, we have investigated the exciton theory of the electronic structure of both semiconducting and metallic nanotubes. We are able to determine quantitatively the exciton energies and exciton binding energies of the nanotubes, in both longitudinal and transverse directions. Our estimate of longitudinal exciton energies and exciton binding energies of semiconducting tubes are the best quantitative fits to the experimental results to date. We also make predictions that the longitudinal exciton binding energies of metallic tubes are comparable to those of semiconducting tubes, in contradiction to recently published results. Our work demonstrates a universality in the photophysics of S-SWCNTs and PCPs that arises from their common quasi-one-dimensionality and π-conjugation.