SCHEDULED MAINTENANCE
Third-order nonlinear optical properties of 3,4-ethylenedioxythiophene copolymers with chalcogenadiazole acceptors†
Abstract
Two 3,4-ethylenedioxythiophene (EDOT) based low band gap donor–acceptor (D–A) conjugated copolymers were designed and synthesized via direct arylation, in which the HOMO–LUMO gaps were fine-tuned by the regular insertion of electron deficient units, 2,1,3-benzothiadiazole (BTZ) and 2,1,3-benzoselenadiazole (BTSe), respectively. Structural characterization was performed by FT-IR, 1H NMR and XPS. In order to investigate the variation in the energy band structure of the copolymers, quantum-chemical calculation using density functional theory was carried out. The alternating insertion of the chalcogenadiazole unit in the PEDOT (poly(3,4-ethylenedioxythiophene)) lowers the HOMO and LUMO energy levels. As a result, the polymers with a lower band gap compared to that of the homopolymer, PEDOT, were obtained. Optical and electrochemical results confirmed that BTSe is marginally superior to BTZ in EDOT based alternate donor–acceptor copolymers. The present experimental results correlate well with HSE06 level theoretical calculations compared to those with the B3LYP level. Z-scan experiments reveal that the copolymers exhibit a strong nonlinear absorption coefficient and a nonlinear refraction coefficient of the order 10−10 esu and the third-order nonlinear susceptibility is of the order of 10−11 esu. These findings indicated that the EDOT–chalcogenadiazole copolymers can be developed into excellent third-order nonlinear optical materials.
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