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

A series of highly polarizable chromophores y1, y2, yz1 and yz2 based on the same bis(N, Ndiethyl) aniline donor, a tricyanofuran acceptor (TCF) and a CF3-Ph-TCF acceptor linked together via thiophene and modified thiophene p-conjugation have been synthesized and are systematically investigated in this paper. Density functional theory (DFT) calculations suggested that the molecular quadratic hyperpolarizability (b) 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 degrees 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 r(33) value of 15.57 x 10(-18) pm cc per (V molecules) and an order parameter of (phi) 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 r(33) value, good thermal stability and high yields suggest the potential use of new chromophores in a nonlinear optical area.