Systematic study on the optimization of a bis(N,N-diethyl)aniline based NLO chromophore via a stronger electron acceptor, extended π-conjugation and isolation groups

Abstract

A series of highly polarizable chromophores A–F based on the same bis(N,N-diethyl)aniline donor, the tricyanofuran (TCF) and CF₃–Ph–TCF acceptor linked via thiophene, alkoxy chain modified thiophene and extended thiophene π-conjugations has been synthesized and systematically investigated. Density functional theory (DFT) calculations suggested that the optimal structure F showed a first-order hyperpolarizability (β) value of 551.0 × 10⁻³⁰ esu which was relatively high for a single molecule. These chromophores showed good thermal stability with their decomposition temperatures all above 220 °C. By doping chromophores A–F with a loading of 25 wt% in amorphous polycarbonate (APC), electro-optic coefficients (r₃₃) up to 149, 139, 148, 142, 252 and 305 pm V⁻¹ at 1310 nm can be achieved, respectively. The normalized r₃₃ value was increased to 19.37 × 10⁻¹⁹ pm cc per (V molecules) for F possessing alkoxy chains as the isolation group, extended thiophene bridge and CF₃–Ph–TCF acceptor, indicating that the isolation groups play an important role in suppressing dipole–dipole interactions especially for those chromophores with super high β values. The largest r₃₃ of 358 pm V⁻¹ was achieved for chromophore F with the doping concentration of 35 wt%. The high r₃₃ value, good thermal stability and good yield suggest the potential use of the new chromophores in nonlinear optical areas.