Nonlinear optical properties of diaromatic stilbene, butadiene and thiophene derivatives

Abstract

Series of highly polar stilbene (1a-e), diphenylbutadiene (2a-c) and phenylethenylthiophene (3a-c) derivatives were preparedviaHorner-Wadsworth-Emmons method with a view to produce new and efficient materials for second harmonic generation (SHG) in the solid-state. The single-crystal X-ray structures of compounds1-3reveal extensive polymorphism and a peculiar photodimerization of the 2-chloro-3,4-dimethoxy-4'-nitrostilbene derivative1ato afford two polymorphs of tetra-aryl cyclobutane4. The stilbene congeners 2-chloro-3,4-dimethoxy-4'-nitrostilbene (1a·non-centro), 5-bromo-2-hydroxy-3-nitro-4'-nitrostilbene (1b) and 4-dimethylamino-4'-nitrostilbene (1e), as well as 4'-fluoro-4''-nitro-1,4-diphenyl-1,3-butadiene (2a) present the ideal, non-centrosymmetric arrangement of the chromophores for nonlinear optical (NLO) activity. Compounds1band2aexhibit only relatively low intensity for second harmonic generation (0.04 and 0.18 times that of urea reference, respectively), while the stilbene polymorph1a·non-centro shows NLO activity of over 32 times that of urea. In addition, the conjugated diaromatic compounds1-3display fluorescence behaviour in CH2Cl2solutions with the exception of stilbene derivative1b.