Symmetric and unsymmetric indolinobenzospiropyran dimers: synthesis and characterization

Symmetric and unsymmetric spiropyran dimers(1-6) have been synthesized. Symmetric spiropyran dimers were synthesized by the one-step reaction of substituted 5,5ʹbisalicylaldehydes (BSA) and Fischerʹs Base derivatives (FB), whereas unsymmetric spiropyran dimers were synthesized in a two consecutive step reaction. The synthesized dyes were characterized by 1H NMR, IR UV-Vis. and mass spectroscopy. UV-Visible spectra of these dimers in excess acid ethanol showed twin absorption maxima at 380¯400 and 460¯480 nm in the visible region, unlikely in the case of bis-spiropyrans which have two merocyanine chromophores connected through a non-conjugated linkage.