Five-membered heteroaromatic hydrazone derivatives for second-order nonlinear optics

The authors synthesized a series of novel five-membered heteroaromatic hydrazone derivatives substituting one phenyl ring by a five-membered heteroaromatic thienyl or furyl ring. Their molecular hyperpolarizabilities and dipole moments were experimentally determined by electric-field-induced second harmonic generation and dielectric measurements, respectively. Values of β_μ of up to 370×10^-40 m⁴V^-1 at 1.907 μm have been obtained. For the first time it is shown that the furan derived π-conjugated core can become the most effective π-conjugated bridge in enhancing the molecular hyperpolarizability when compared with the corresponding phenyl and thienyl counterparts if an appropriate electron donor and acceptor are used. The macroscopic nonlinearity of the novel crystalline hydrazone derivatives has been investigated by the Kurtz and Perry powder test showing second harmonic activities up to 2-3 orders of magnitude higher than that of urea.