Dimethylaminocyanobiphenyl (DMACB): A new optimized molecular crystal for quadratic nonlinear optics in the visible

Abstract

The linear and quadratic nonlinear optical properties of a new organic crystal, 4,4′-dimethylaminocyanobiphenyl (DMACB) are reported. Its dominant second-harmonic generation and electrooptic tensor coefficients are estimated to be respectively d 33 = 240 pm V −1 and r 33 = 570 pm V −1 at static frequencies. The crystal is furthermore fully transparent in the visible up to its solid-state absorption cut-off at 420 nm. Such “optimal” trade-off between transparency and nonlinear efficiency may prove adequate for the generation of blue light by second-harmonic generation from the near IR. Both spectral and nonlinear properties of DMACB are related to the twisted elongated structure of the asymmetric charge-transfer moiety and to the extremely anisotropic structure of the crystalline packing. An excitonic coupling scheme is suggested to be responsible for the extended transparency of DMACB as compared to crystals, such as POM, with a more isotropic packing.