Highly Nonlinear Optical Configurationally Locked Triene Crystals Based on 3,5-Dimethyl-2-cyclohexen-1-one

New organic nonlinear optical configurationally locked polyene (CLP) crystals based on 3,5-dimethyl-2-cyclohexen-1-one have been designed and their supramolecular organization investigated. Acentric single crystals 2-(5-methyl-3-(4-(pyrrolidin-1-yl)styryl)cyclohex-2-enylidene)malononitrile (MH2) of large sizes with a maximal side length of up to 1 cm have been grown from acetonitrile solution. The acentric MH2 crystals present the monoclinic space-group symmetry Cc and exhibit a large macroscopic nonlinearity with a similar powder second-harmonic generation efficiency at 1.9 µm as the well-studied DAST (N,N-dimethylamino-N′-methylstilbazolium p-toluenesulfonate), which is about seven times larger than that of analogous CLP crystals studied previously. The microscopic and macroscopic nonlinearities are also investigated theoretically using quantum chemical calculations.