Spectroscopic and photochemical evaluation of stereochemically biased 3'-substituted spiropyran photoswitches.

Three series of spiropyran photoswitches with an auxiliary chiral centre at position 3' of the indoline unit were synthesized. Using one example, a novel methodology for synthesis of an optically active spiropyran photoswitch with a defined chirality at position 3' is demonstrated. Furthermore, a new acid-mediated strategy for spiropyran purification affording moderate to excellent yields (up to 96%) is reported herein.