A closed-ring dithienylethene and its Ag(I) complex: Syntheses, structures, and reversible photochromism

A new cyano-equipped dithienylethene in closed-ring form (L-c) was first isolated and structurally characterized by IR, H-1 NMR, and X-ray single-crystal diffraction. It showed an interesting racemic mixture of R, R and S, S enantiomer pairs evidencing the structural transformation from 1,3,5-hexatriene to cyclohexadiene in the photochemical conrotatory cyclization. Followed UV-Vis spectral investigations exhibited its reversible photochromism in both THF solution and solid state with the maximum absorption wavelength of 607 nm observed in the visible band. The photo-isomerization kinetics of the compound indicated a first-order process for photo-reversion and zeroth-order for photo-cyclization. The compound was further used as a ligand to self-assemble with Ag(CF3SO3) resulting in complex 1. Its structure was characterized by elemental analysis, IR, H-1 NMR, and ESI-MS. Complex 1 demonstrated reversible photochromism in the solid state with the same lambda(max) as the closed-ring ligand. Unlike the complex derived from the open-ring ligand, Ag(I) ions coordination with the closed-ring ligand doesn't modify the absorption due to the restricted free rotation of the thienyl rings in the rigid configuration of the closed-ring ligand. In comparison with the open-ring ligand, 1 displayed a faster photo-isomerization rate corresponding to the smaller band gap determined by cyclic voltammetry.