Understanding excitons in optically active polymers

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, A_g–B_u crossing in polyenes and common 1/N energy dependencies in oligomers. Copyright © 2007 Society of Chemical Industry