Synthesis and properties of thermo- and photochromic bisindolinobenzospiropyrans linked by thio- and carbonyl groups

Novel thermo- and photochromic thio- and carbonylated bisspiropyrans have been synthesized by the reaction of 5,5ʹthiobissalicylaldehydes or the 5,5ʹ-carbonyl analogue and Fischerʹs base derivatives in 1:2.5 mole ratios. For the synthesis of 5,5ʹ-thio- or carbonylbissalicylaldehyde, 4,4ʹ-thiodiphenol or 4,4ʹ-carbonylbisphenol was formylated with paraformaldehyde. The synthesized dyes were characterized using 1H NMR, IR, UV¯vis and mass spectroscopy. The thio-bisspiropyrans showed no thermo- and photochromism whereas the carbonylated dyes showed weak thermo- and photochromism.