Synthesis and Photochromic Properties of 2-(3-Nitro-2-pyridylmethyl)benzazoles

摘要

2-(3-NItro-2-pyridylmethyl)benzazoles were synthesized, and their photochromic properties were studied by flash photolysis. Introduction of a nitropyridyl istead of the nitrophenyl moiety into the 2-methyl group insignificantly increases the basicity of the methyloene group. Nitropyridyl-substituted benzazoles give rise to three detectable photoinduced forms: the corresponding anion at pH > 10, azamerocyanine at pH approx 4, and monomethinecyanine at pH approx = 1. Irradiation of solutions of weakly basic benzoxazole and benzothiazole derivatives at pH approx = 4 results in formation of neutral chelate structures in which the hydrogen atom is linked simultaneously to two nitrogen atoms: one in the pyridine ring, and the second, in the azole ring.