Synthesis and study of new photochromic spiropyrans modified with carboxylic and aldehyde substituents

Three new photochromic spiropyrans containing a carboxylic group in the indoline fragment and an aldehyde substituent in the [2H]-chromene moiety were synthesized. The structure of the compounds obtained was studied using H-1 and C-13 NMR, IR and elemental analysis. Single crystal X-ray analysis was used to refine the molecular structure of 8'-formyl-1,3,3,6'-tetramethyl-spiro[indoline-2,2'-2H-chromene]-5-carboxylic acid. It was found out that in the solid state the molecules of that compound are arranged in dimeric associates due to the formation of intermolecular hydrogen bonds between carboxylic groups of two adjacent molecules. All the spiropyrans were shown to be photochromic with the lifetimes of the open forms in the range of 1.5-46.0 s. (C) 2019 Elsevier B.V. All rights reserved.