Effects of heteroaryl ring on the photochromism of asymmetrical diarylethenes containing a naphthalene group.

Photochromic asymmetrical diarylethene derivatives 1o-4o bearing different benzo-five-membered heterocyclic rings were synthesized and characterized with single-crystal X-ray diffraction microscopy. The effects of heterocyclic ring on their properties including the photochromic behaviors in solution, solid state and crystalline phase were systematically investigated. The diarylethenes bearing benzothiophene or indole ring exhibited high cyclization quantum yields in solution, and evidently enhanced the fluorescent modulation efficiency in solid state, while those containing benzofuran or thiophene ring exhibited the opposite behaviors. In addition, indole ring red-shifted the absorption maximum, and notably enhanced the fatigue resistance of the diarylethene. These results indicate that heteroaryl ring played an important role in the photoisomerization of these diarylethenes, causing the heterocyclic effect.