The reaction between malononitrile dimer and 1,3-dithiole-derived polyenals affords push–pull systems with (Z)-geo-metry around the newly formed C@C bond. In one instance, an unexpected shortening of the merocyanine chain takes place. These push–pull derivatives have weakly alternated structures and moderate optical nonlinearities, which can be modified by functional-ization of the amino group. 2-Amino-1,1,3-tricyanopropene (malononitrile dimer, 1) 1,2 is a multifunctional molecule with a rich chemistry, which has allowed the preparation of new dyes 3,4 and chromoionophores, 5 among many other structures. To that end, the reactivity of 1 towards aromatic aldehydes has been widely explored, 3,5–8 whereas heterocyclic alde-hydes have only seldom been used, 4,9,10 and there are very few examples of Knoevenagel reactions of 1 with a,b-unsaturated aldehydes. 4,11 Moreover, polycyano acceptor groups have been widely used in the search for new compounds with second-order nonlinear optical (NLO) properties, 12,13 and 1 is structurally related to the very successful acceptor 2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran (TCF), 14 but, unlike the latter compound, the NLO properties of merocyanines derived from 1 have received a very limited attention. 7,8,11 In this Letter, we report the synthesis and full stereo-chemical characterization of push–pull compounds 2 (Fig. 1), bearing a proaromatic 1,3-dithiole donor unit, 15,16 along with their electrochemical, linear and nonlinear optical properties. The latter are compared to those of related merocyanines bearing other poly-cyano acceptors.