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

Three azo dyes with a thiazole based donor-π-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. [Display omitted] ► Novel donor-π-acceptor thiazole azo dyes (a–c) as NLO chromophores have been synthesized. ► Single crystal X-ray and thermal properties of dyes a–c have been investigated. ► Linear and NLO properties of dyes a–c have been studied. ► Dye c shows the largest NLO response compared with dyes a and b. ► Dyes a–c represent interesting examples of asymmetrical 2D charge transfer chromophores.