Structure and Photochromic Properties of New Spiropyrans of Indoline Series Containing Free Carboxylic Groups

Abstract

Two new photochromic spiropyrans containing carboxyl groups in the hetarene part of the molecule and being of interest as modifiers of organometallic scaffolds to give them photo-controlled functions are obtained by the cyclocondensation reaction of 5-carboxy-1,2,3,3-tetramethyl-3H-indolium iodide with corresponding 2,4-diformylphenols. The structure of the compounds obtained is confirmed by infrared (IR), 1H and 13C NMR spectroscopy (using 1H–1H COSY, 1H–13C HSQC, 1H–13C HMBC, and 1H–15N HMBC 2D NMR techniques); the chemical composition is determined by elemental analysis. The diffraction patterns of powdered samples of the compounds are measured, which make it possible to determine the symmetry groups and unit-cell parameters. Photochemical studies reveal the photochromic properties of the compounds at room temperature, and measurement of the rate constants kBA of the thermal discoloration of merocyanine forms at different temperatures allowed us to calculate the activation energy of these processes.