Photochromic properties of triangle terthiophene- and triphenylamine-configured diarylethene type dye with propeller-like conformation

A photochromic dye (TPDA) with helical structure was configured by attaching triangle terthiophene to triphenylamine units. It exhibits typical photochromic behavior when irradiated with UV (390 nm)/visible light (> 410 nm). Moreover, TPDA in tetrahydrofuran (THF) can be switched alternately between color and colorless state. In addition, it exhibits highly emissive character in THF and could emit bright blue fluorescence by UV irradiation. And the fluorescence emission efficiency was estimated to be 0.41. Under the UV light irradiation, a ring-closure reaction occurred and the blue fluorescence was quenched effectively at the same time. At photo-stationary state, the quantum yield was lowered to 0.10. Therefore, a switch controllable fluorescence “on–off” molecular system was developed when light irradiation cycle established (UV/visible light). Optimization of the dye structure was performed using density functional theory at the DND/B3LYP level of theory. The structural analysis reveals that the shorter distance between reactive atoms (< 4.2 Å) in the triangle terthiophene unit promotes the smoothly photochromism of TPDA.