Intramolecular hydrogen bonding in a triangular dithiazolyl-azaindole for efficient photoreactivity in polar and nonpolar solvents

Abstract

A triangular dithiazolyl-azaindole derivative has been synthesized as a highly sensitive photochromic molecule. 2,4-Dimethyl-5-phenylthiazol derivative 1a, and a reference compound, 5-methyl-2-phenylthiophene derivative 2a, both showed photochromism with quantum yields of 90 and 45%, respectively, in hexane, and 90 and 35%, respectively, in methanol. In the single-crystal state, 1a revealed photochromic coloration. Its conformation was assigned to a photoreactive state with C2-symmetry around the hexatriene reaction center. Temperature-dependent NMR studies and quantum chemical calculations indicated the contribution of intramolecular hydrogen-bonding between the central azaindole unit and the side thiazole units, which stabilizes the photoreactive C2-symmetric conformation and elevates the photoreactivity in both non-polar and polar solvents. Photochromic dithiazolyl-azaindole is brought into a conformation that is favorable for photocyclization through intramolecular CH-N interactions. A remarkable photocyclization quantum yield was observed both in polar and non-polar solvents. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.