The design and synthesis of nonlinear optical chromophores containing two short chromophores for an enhanced electro-optic activity

Abstract

A series of nonlinear optical chromophores A–D based on the diethylaminophenyl donor and tricyanofuran or phenyl-trifluoromethyl-tricyanofuran acceptors coupled through a tetraene bridge was synthesized and investigated. In particular, the donor and bridge sections of chromophores B and D were functionalized with a small chromophore alkylaniline cyanoacetate (B1) and dialkylaminobenzylidene malononitrile (D1) group, respectively, compared to the pentafluorobenzene group of chromophores A and C. Before poling, two small chromophores B1 and D1 with large dipole moment will greatly weaken the electrostatic interaction between chromophores by steric effect and electrostatic screening effect, thus increasing the poling efficiency. Although density functional theory calculations suggested that they have similar first-order hyperpolarizability, polymeric thin films doped with chromophores A–D exhibited the different r₃₃ values of 115, 166, 213 and 276 pm V⁻¹ at 1310 nm, respectively. The normalized r₃₃ value of chromphores B and D was up to 7.72 × 10⁻¹⁹ and 17.25 × 10⁻¹⁹ pm cc per (V molecules), which is much higher than that of chromophores A and C. All these prove that introducing a small chromophore into the main chromophore can greatly improve the electro-optic coefficient of the chromophore by a rational molecular design.