Thiazole azo dyes with lateral donor branch: Synthesis, structure and second order NLO properties

Three azo dyes with a thiazole based donor-pi-acceptor structure containing a methoxyphenyl group as the lateral donor branch were synthesized and fully characterized. The formyl azo dye precursor was synthesized using 5-formylaminothiazole derivative as the diazo component and N,N-diethylaninline as the coupling component. Knoevenagel condensation of this precursor with different acceptors, namely, indandione, malononitrile and dicyanovinylindanone afforded the desired nonlinear optical chromophores a-c, respectively. The optical property, thermal stability and second order nonlinear optical activity were evaluated and a single crystal structural characterization was performed for two of the dyes. All nonlinear optical dyes a-c have good nonlinearity and good thermal stability. Compared with dyes a and b, dye c shows more than triple second order nonlinear optical response, the result that makes this molecule an unusual example of asymmetrical 2D charge transfer chromophore.