Thiacrown Ether Substituted Styryl Dyes:  Synthesis, Complex Formation and Multiphotochromic Properties

Syntheses of two series of new styryl dyes incorporating thiacrown ether moieties (CSDs 3a−e, 4a−e) are described. 1H NMR and UV−vis measurements show that these compounds exhibit a strong preference for formation of complexes with heavy metal ions. Polarographic measurements allow conversion of relative complex formation stability constants, determined spectrophotometrically, into absolute values. The photochromic properties of the CSDs are based on reversible trans-cis isomerization and [2+2]-photocycloaddition. The influences of the terminal group of the N-substituent and of the size and composition of the crown ether cavity on metal cation complexation selectivity and on photochromism are evaluated.