Theoretical Investigations on the Electronic and Optical Properties of Luminescent Poly(alkylthiophene‐co‐pyridine)

Abstract

AbstractQuantum‐chemical techniques were applied to investigate a series of conjugated polymers: poly(3‐octylthien‐2,5‐ylene‐co‐pyrid‐2,6‐ylene) (p1), poly[pyrid‐2,6‐ylenebis(3‐octylthien‐2,5‐ylene)] (p2) and poly[pyrid‐2,5‐ylene‐ bis(3‐octylthien‐2,5‐ylene)] (p3) comprising alternating π‐excessive 3‐alkylthiophene and π‐deficient meta‐ or para‐linked pyridine moieties. Their ground state and excited state structures were optimized with density functional theory B3LYP method, and the optical properties were calculated by the time‐dependent density functional theory (TD‐DFT) and ZINDO/S methods. Their HOMO‐LUMO gaps (ΔH‐L), the lowest excitation energies (Eex), ionization potentials (IP) and electron affinities (EA) were obtained by extrapolating those of the polymers to the inverse chain length equal to zero (1/n=0). The calculated results showed that the decrease of pyridylene content increased the HOMO level and decreased the LUMO level while the para‐linkage further contributed to it. The IP are in the order: p1>p2>p3 but EA are: p1<p2<p3. In addition, the decrease of the pyridylene content and the para‐linked pyridylene in the backbone of the polythiophene resulted in a narrowed energy gap and bathochromic absorption and emission peaks.