Theoretical and experimental investigations on the photoconductivity and nonlinear optical properties of donor–acceptor π conjugated copolymer, poly(2,5-(3,4-ethylenedioxythiophene)-alt-2,7-(9,9-dioctylfluorene))

Abstract

The donor–acceptor (D–A) π conjugated copolymer, poly(2,5-(3,4-ethylenedioxythiophene)-alt-2,7-(9,9-dioctylfluorene)) (P(EDOT–FL)), a photoconductive and nonlinear optical material has been synthesized via, a direct arylation method using palladium acetate as a catalyst and characterized. The theoretical studies along with photophysical and electrochemical studies confirmed that the copolymer exhibited a relatively lower band gap (2.29 eV) than that of polyfluorene. The photoconductivity properties of the P(EDOT–FL):PC₆₁BM films under various illuminations were studied and high photosensitivity was observed at 488 nm. The field dependence of the photoconductivity in P(EDOT–FL):PC₆₁BM blend films showed that the films could withstand up to 75 V μm⁻¹ and the photosensitivity at higher electric fields was even greater than two lakh (at 75 V μm⁻¹, the photosensitivity was 289 742). At higher electric fields, the photocurrent entered into micro ampere ranges. The intensity dependence on the photocurrent in these films was also investigated. Third-order nonlinear optical properties of P(EDOT–FL) under nanosecond laser excitation at 532 nm have been studied by a Z-scan technique. The polymer exhibited a high nonlinear absorption and refraction coefficient. The polymer also showed a good optical limiting response at 532 nm. These results provide an avenue for application of P(EDOT–FL) in photo conducting and nonlinear optical devices.