Enhanced electro-optic activity from the triarylaminophenyl-based chromophores by introducing heteroatoms to the donor

Abstract

A series of chromophores T1–T3 based on the same thiophene π-conjugation and tricyanofuran acceptor (TCF) but with different heteroatoms in the triarylaminophenyl (TAA) donors have been synthesized and systematically investigated in this study. Density functional theory (DFT) was used to calculate the HOMO–LUMO energy gaps and first-order hyperpolarizability (β) of these chromophores. Moreover, to determine the redox properties of these chromophores, cyclic voltammetry (CV) experiments were performed. After introducing the heteroatom to the benzene ring of the TAA donor, reduced energy gaps of 1.28 and 0.84 eV were obtained for chromophores T2 and T3, respectively, which was much lower than for chromophore T1 (ΔE = 1.46 eV). These chromophores showed excellent thermal stability with their decomposition temperatures all above 280 °C. Compared with results obtained from the chromophore without the heteroatom (T1), these new chromophores show better intramolecular charge-transfer (ICT) absorption. Most importantly, the high molecular hyperpolarizability (β) of these chromophores can be effectively translated into large electro-optic (EO) coefficients (r₃₃) in the poled polymers. The electro-optic coefficient of poled films containing 25 wt% of these new chromophores doped in amorphous polycarbonate (APC) afforded values of 16, 58 and 95 pm V⁻¹ at 1310 nm for chromophores T1–T3, respectively. High r₃₃ values indicated that introducing heteroatom to the benzene ring of the TAA donor can efficiently improve the electron-donating ability, which improves the hyperpolarizability (β). The long-chain on the benzene ring of the TAA donor, acting as the isolation group, may reduce intermolecular electrostatic interactions, thus enhancing the macroscopic EO activity. These properties, together with the good solubility, suggest the potential use of these new chromophores as advanced material devices.