Understanding excitons in optically active polymers

Abstract

We review the solid‐state physics approach to electronic and optical properties of conducting polymers, and bring together the languages of solid‐state theory for polymers and the quantum chemistry of oligomers. We consider polymers as generic one‐dimensional semiconductors with specific features of strongly correlated electronic systems. Our model combines the large distance electron–hole motion within an exciton, governed by long‐range Coulomb attraction with strong intramonomer electronic correlations, which results in effective intramonomer electron–hole repulsion. We exploit the dielectric screening to go beyond the single chain picture and to compare excitons for polymers in solutions and in films. Our approach allows the connecting, explaining, exploiting and organizing of such different experimental and numerical findings as shallow singlet and deep triplet excitons in phenylenes, anomaly in singlet–triplet exciton formation ratio, Ag–Bu crossing in polyenes and common 1/N energy dependencies in oligomers. Copyright © 2007 Society of Chemical Industry

New tools for the systematic analysis and visualization of electronic excitations. I. Formalism

“…In such cases, the excited state is viewed as a quasi-particle (exciton), whose internal structure is determined by the electron-hole separation and the exciton binding energy. 22,23 The two views can be reconciled when considering an underlying two-body wavefunction of the exciton. This idea is illustrated in Fig.…”

Commentary: Carbon Nanotubes, CdSe Nanocrystals, and Electron−Electron Interaction

“…11,12 In comparison with these species, SWNTs have the great advantage of being structurally rigid with very rare structural defects. Rigidity in SWNTs creates high mobility for free carriers and excitons, with the concomitant weak Franck-Condon coupling of these species to nanotube vibrations.…”

Block copolymer strategies for solar cell technology

“…OPVs, on the other hand, have higher exciton binding energies and, therefore, excitons must reach a material interface with a lowest unoccupied molecular orbital (LUMO) offset to produce separated electrons and holes. 21 The photovoltaic mechanism in organic devices has been discussed at length in the literature, 19,[22][23][24][25][26][27][28][29] therefore, here, we only briefly outline the process for readers new to the field. Figure 1 shows the individual steps involved in the dominant process that converts light into an electrical current: (i) the incoming photon excites an electron from the HOMO to the LUMO of the donor material to (ii) create an exciton, (iii) which traverses the donor material to a donor-acceptor interface where (iv) the excited electron separates from its bound hole onto the LUMO of the acceptor.…”

“…19,20 Inorganic materials have low exciton binding energies such that photoexcitation spontaneously creates a separate free electron and a free hole (a hole being a positive charge located within the material's highest occupied molecular orbital, HOMO), which can both travel directly to their respective electrodes. OPVs, on the other hand, have higher exciton binding energies and, therefore, excitons must reach a material interface with a lowest unoccupied molecular orbital (LUMO) offset to produce separated electrons and holes.…”