THERMALLY IRREVERSIBLE PHOTOCHROMIC SYSTEMS - PHOTOREACTION OF DIARYLETHENE DERIVATIVES WITH IMIDAZO[1,2-A]PYRIDINE RINGS

A non-symmetrical diarylethene with imidazo[1,2-a]pyridine ring on one end and thiophene ring on the other end, 1,2-dicyano-1-(2-methylimidazo[1,2-a]pyridin-3-yl)-2-(2,4,5-trimetyl-3-thienyl)ethene 2Z underwent a hexatriene-cyclohexadiene type reversible ring-closure reaction by photoirradiation, while an only Z-E isomerization was observed for a symmetrical diarylenthene with two imidazo[1,2-a]pyridine rings, 1,2-dicyano-1,2-bis(2-methylimidazo[1,2-a]pyridin-3-yl)ethene 1Z. The ring-closure reaction was not discerned. The photogenerated closed-ring form 2C had the absorption band at 535 nm, which is 23 nm longer wavelengths than that of the corresponding dithienylethene, and kept the absorption intensity constant for more than 24 h at 80-degrees-C. The quantum yield close to unity was observed for the photochemical ring-opening reaction of 2C with 546 nm light.