As derivatives of 1-methyl-4-[2-[4-(dimethylamino)phenyl]ethenyl]pyridinium p-toluenesulfonate (DAST), several oligoene compounds with (dimethylamino)phenyl and pyridinium groups at both ends were synthesized for efficient terahertz-wave generation using second-order nonlinear optical (NLO) effects, Appropriate Solubility necessary for solution crystal growth was provided to these compounds by introducing ethyl groups instead of methyl groups attached so far. More than 20 out of 63 crystals were found to have second-order NLO properties. (c) 2008 Elsevier B.V. All rights reserved.