Study on the second-order optical behavior of 4-(substituted-benzylidene)-2-phenyl-4H-oxazol-5-one.

The maximum absorption wavelengths (lambda(a-max)), absorption coefficient (epsilon), maximum emission wavelengths (lambda(e-max)) of 4-benzo[1,3]dioxol-5-ylmethylene-2-phenyl-4H-oxazol-5-one (1), 4-(3,4-dimethoxybenzylidene)-2-phenyl-4H-oxazol-5-one (2) and 4-(3,4,5-trimethoxy-benzylidene)-2-phenyl-4H-oxazol-5-one (3) were measured, their second-order nonlinear polarization values (beta(xxx)) were determined by solvatochromic method. Although the spectral nature (lambda(a-max), epsilon, lambda(e-max)) and beta(xxx) values of 1, 2 and 3 were close to each other in the same solvent, the second-order harmonic generation (SHG) value of sample 1 is higher obviously than that of sample 2 or 3 in solid state. The crystal structures of 1 and 2 characterized by single crystal X-ray diffraction technique indicated the reason why the SHG value of 1 is higher.