Organic Phenolic Configurationally Locked Polyene Single Crystals for Electro-optic and Terahertz Wave Applications

We investigate a configurationally locked polyene (CLIP) crystal 2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (OH1) containing a phenolic electron donor, which also acts as a hydrogen bond donor. The OH1 crystals with orthorhombic space group Pna2(1) (point group mm2) exhibit large second-order nonlinear optical figures of merit, high thermal stability and very favorable crystal growth characteristics. Higher solubility in methanol and a larger temperature difference between the melting temperature and the decomposition temperature of OH1 compared to analogous CLP crystals, are of advantage for solution and melt crystal growth, respectively. Acentric bulk OH1 crystals of large sizes with side lengths of up to 1 cm with excellent optical quality have been successfully grown from methanol solution. The microscopic and macroscopic nonlinearities of the OH1 crystals are investigated theoretically and experimentally. The OH1. crystals exhibit a large macroscopic nonlinearity with four times larger powder second harmonic generation efficiency than that of analogous CLP crystals containing dimethylamino electron donor. A very high potential of OH1 crystals for broadband THz wave emitters in the full frequency range of 0.1-3 THz by optical rectification of 160 fs pulses has been demonstrated.