The first push–pull 1,3-dithiol-2-ylidene derivatives containing an azine spacer have been prepared in order to evaluate the effect of the azine bridge on the second-order NLO properties of these compounds, which show µβ(0) values lower than those of similar derivatives endowed with ethylenic spacers. The linear and nonlinear optical properties of these compounds have been studied both experimentally and theoretically by TD-DFT and ab initio CPHF calculations respectively. Moreover, the E–Z photoisomerization of one of these azines is reported.
