Insights into the photo- and thermal induced intramolecular processes of 2-(hydroxyphenyl)benzoxazoles: Experimental and theoretical aspects

It has been established that 2-(2-carboisopropoxy-3,4-dichloro-6-hydroxyphenyl)benzoxazole exhibits solvatochromic properties due to keto-enol equilibrium through reversible GSIPT processes. The photoinitiated processes occurring in the studied molecules of the 2-(2-hydroxyphenyl)benzoxazole are determined by their isomeric form. In the case of enol forms, photoexcitation leads to ESIPT processes accompanied by fluorescence with an anomalous Stokes shift. While the keto forms exhibit negative T-type photochromism due to reversible ZE photoisomerization. It was found that the thermal keto-enol equilibrium is completely determined by specific interactions with the solvent. On the reaction pathways associated with the excited state proton transfer and further structural transformations on the S1 potential energy surface, twisted intermediates (TICT state) were found that specify various channels for the deactivation of the excited state. Based on the results obtained, the mechanisms of photoinduced processes in heptane and DMSO are proposed. In strong proton acceptor solvents DMSO and DMF, along with the keto-enol tautomeric rearrangement, an equilibrium of dissociation of HBO molecules with the formation of anionic forms was revealed.

Automated summary

It has been established that the photoinitiated processes in 2-(2-hydroxyphenyl)benzoxazole are determined by its isomeric form, with enol forms leading to ESIPT processes and keto forms exhibiting negative T-type photochromism. The thermal keto-enol equilibrium is found to be influenced by specific interactions with the solvent. The study also reveals twisted intermediates (TICT state) on the S1 potential energy surface that play a role in the deactivation of the excited state, and proposes mechanisms for photoinduced processes in heptane and DMSO.