The Effect of Substituent‐Dependent Photoinduced Intramolecular Charge Transfer on the Photochromism of Hemithioindigos. Issue 11 (23rd August 2017) - Wang, Junjie
Abstract: A series of N, N′ ‐diarylamine‐modified hemithioindigos (HTIs) were synthesized and characterized. Photochemical Z / E isomerization around the C=C double bond occurred for all novel HTIs in various solvents. Due to a strong donor–acceptor π‐conjugated structure, the novel HTIs exhibited a strong red shift and clear solvatochromism in steady‐state absorption and fluorescence spectroscopic measurements, respectively. An intramolecular charge transfer (ICT) from the diarylamine‐substituted stilbene component (donor) to the thioindigo part (acceptor) strongly affects the isomerization behavior. HTI is the dominating photochromic unit in this system but the substitution pattern on the triarylamine (TAA) moiety causes unusually strong changes in the photostationary states (PSS) and thermal stabilities. Electron‐withdrawing substituents (such as cyano groups) strongly improve thermal stabilities and enrich the E ‐isomer content in the photostationary state, however electron‐donating substituents play a converse effect, for example, in the solvents hexane and tetrachloroethene. The low E ratio in the PSS in more polar solvents, such as acetonitrile, can be explained by a very fast thermal back reaction and formation of a new decay state in OMe‐substituted compounds. Abstract : Twist and shout : The photoisomerization and thermal stabilities of hemithioindigos (HTIs) can be modulated by N, N′ ‐diarylamine substitution at the stilbene moiety, furnishing a donor–acceptor system. In contrast to typical HTI substitution effects, electron‐withdrawing groups in the triarylamine (TAA) moiety lead to a red‐shift of the absorption band maxima, whereas substitution with an electron‐donating group (OMe) promotes TICT state population.