Photoinduced absorption in disubstituted polyacetylenes: Comparison of theory with experiments

Abstract

In a recently performed experiment, [Korovyanko Phys. Rev. B 67, 035114 (2003)] have measured the photoinduced absorption (PA) spectrum of phenyl-disubstituted polyacetylenes (PDPA's) from the 1B(u) and 2A(g) excited states. In the 1B(u) PA spectrum they identified two main features, namely, PA1 and PA2, while in the 2A(g) spectrum they identified only one feature called PA(g). In this paper we present a theoretical study of the 1B(u) and 2A(g) PA spectra of oligo-PDPA's using the correlated-electron Pariser-Parr-Pople model and various configuration interaction methodologies. We compare the calculated spectra with the experiments, as well as with the calculated spectra of polyenes of the same conjugation lengths. The calculated spectra are in good agreement with the experiments. Based upon our calculations, we identify PA1 as the mA(g) state and PA(g) as the nB(u) state of the polymer. Regarding the PA2 feature, we present our speculations. Additionally, it is argued that the nature of the excited states contributing to the 2A(g)-PA spectra of oligo-PDPA's is qualitatively different from those contributing to the spectra of polyenes.