Synthesis of unsymmetrical 2-(2-vinyl-4H-chromen-4-ylidene)malononitrile dyes via Knoevenagel reaction.

• New potential chromene based non-linear optical (NLO) dyes were prepared. • The benzopyran fragments is a very promising acceptor for design of NLO chromophores. • High values of the first hyperpolarizability achieved for benzopyran chromophores. • Reversible solvatochromism was obtained for chromene-based chromophores. A series of new chromophores based on 4-(dicyanomethylene)-2-vinyl 4H-chromenes was synthesized and their physical properties (UV–Vis, NMR, mass spectrometry) were studied. The chromophores show moderate or good solubility in organic solvents. Solvatochromism was investigated for compounds in solvents of low (1.4-dioxane, chlorobenzene, methylene chloride) and high polarity (acetone, acetonitrile). The calculations of the first hyperpolarizability (β) was performed using M052X/6-31+G(d) approximation. Chromophore's molecules are characterized by high calculated values of the first hyperpolarizability (β) that is only 15% lower than that of FTC analogs. [ABSTRACT FROM AUTHOR]