Photophysics of phenyl-substituted polyacetylenes, theory

We present a theoretical study of the electronic structures of poly-phenylacetylene (PPA) and poly-diphenylacetylene (PDPA). Strong photoluminescence (PL) in PDPA’s is a consequence of the occurrence of the 2Ag two-photon state above the optical 1Bu, in spite of the polyene backbone. This reversed energy ordering (as compared to linear polyenes and trans-polyacetylene, t-PA) is a signature of reduced effective electron correlations in PPA and PDPA. The optical gaps of the substituted materials are smaller than polyenes of the same chain length.