Enhancement of electro-optic properties of bis(N,N-diethyl)aniline based second order nonlinear chromophores by introducing a stronger electron acceptor and modifying the π-bridge

Abstract

A series of highly polarizable chromophores y1, y2, yz1 and yz2 based on the same bis(N,N-diethyl)aniline donor, a tricyanofuran acceptor (TCF) and a CF₃-Ph-TCF acceptor linked together via thiophene and modified thiophene π-conjugation have been synthesized and are systematically investigated in this paper. Density functional theory (DFT) calculations suggested that the molecular quadratic hyperpolarizability (β) value of the CF₃-Ph-TCF based chromophore is 16.8% (yz1 compared with y1) and 46.8% (yz2 compared with y2) larger than those TCF based chromophores. These chromophores showed good thermal stability and their decomposition temperatures were all above 230 °C. Compared with the results obtained from the chromophores (y1 and y2) with the TCF acceptor, the new chromophores (yz1 and yz2) with the CF₃-Ph-TCF acceptor show better intramolecular charge-transfer (ICT) absorption (108 nm and 97 nm red-shift). By doping chromophores y1, y2, yz1 and yz2 with a high loading of 25 wt% in amorphous polycarbonate (APC), electro-optic (EO) coefficients (r₃₃) of up to 149, 139, 142 and 252 pm V⁻¹ at 1310 nm can be achieved, respectively. A normalized r₃₃ value of 15.57 × 10⁻¹⁸ pm cc per (V molecules) and an order parameter of (Φ) up to 27.3% was obtained for yz2 possessing the bis(N,N-diethyl)aniline donor, the alkoxy chain modified thiophene bridge and the CF₃-Ph-TCF acceptor, which indicated that the structure–property relationship was essential. The high r₃₃ value, good thermal stability and high yields suggest the potential use of new chromophores in a nonlinear optical area.