Synthesis and third-order nonlinear optical properties of low band gap 3,4-ethylenedioxythiophene-thiophene copolymers

Abstract

Alternate donor–acceptor 3,4-ethylenedioxythiophene (EDOT) based copolymers with thiophene and 3-methyl thiophene were designed by employing density functional theory (DFT) in the periodic boundary condition using HSE06 exchange correlation functional and 6-31G basis set. The designed copolymers were synthesized via a simple and facile route, i.e., direct arylation and their third-order nonlinear optical properties were investigated by Z-scan technique. The resultant copolymers, P(EDOT-THP) and P(EDOT-MeTHP) were characterized by spectroscopic analysis. The photophysical and electrochemical properties of EDOT-thiophene copolymers were investigated by UV–visible spectra and cyclic voltammetry, respectively. The copolymers revealed low band gap and better electronic properties as compared to the homopolymers. The introduction of EDOT unit in the polythiophene leads to decreased HOMO-LUMO energy levels, and the absorption spectra was red shifted when compared with that of the parent compound. The nonlinear absorption and nonlinear refraction coefficient of copolymers have been investigated at 532 nm. The optical limiting properties of copolymers have also been measured. The copolymers exhibited strong optical nonlinearity owing to the presence of alternate donor-π-acceptor scheme in the polymers.