D–π–A solvatochromic charge transfer dyes containing a 2-cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran acceptor

The preparation and solvatochromic behavior of novel, intramolecular charge transfer dyes obtained by the condensation of 2-cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran with 4-dimethylamino benzaldehyde and 9-formyljulolidine are described. The absorption and fluorescence emission spectra of the dyes were studied in solvents of differing polarity. The dyes exhibited positive solvatochromism and their solvatochromic properties are discussed with the aid of semiempirical calculations. The HOMO and LUMO values of the dyes were obtained using both cyclic voltammetry and theoretical calculations; the electrochemical results were in agreement with both observed values and theoretical calculations. pH molecular switching was achieved by modulation of intramolecular charge transfer by means of protonation/deprotonation in DMSO solution.