Engineering of non-linear optical crystals displaying a quasi perfect polar alignment of chromophores

Four non-linear optically active crystals based on organic salts obtained b y bis-protonation of four diamines (trans-(+/-)-1,2-, trans-(1R,2R)-(-)-, c is-1,2-diaminocyclohexane or R-(-)-2-methylpiperazine) by 2-methoxy-4-nitro phenol have been prepared. Their crystal structures and non-linear optical efficiencies have been studied. The two adjacent proton acceptor sites in 1 ,2-diaminocyclohexanes play an important role in aligning the 2-methoxy-4-n itrophenolate chromophores in a quasi-perfect polar arrangement by anchorin g through short hydrogen bonds. In the case of the methylpiperazinium deriv ative the symmetrical 1,4 location of proton acceptor sites directs the chr omophores to near antiparallel alignment by forming short hydrogen bonds. T he second harmonic generation efficiencies at 1.064 mu m of Nd3+:YAG laser light are equivalent to that of POM (3-methyl-4-nitropyridine-1-oxide) for the three diammoniocyclohexane derivatives and equivalent to twice that of urea for the methylpiperazinium derivative.