Effects of substituted chalcogen atoms on excited state proton transfer reaction for 2,5-bis(benzoxazole-2-yl)-thiophene-3,4-diol derivatives: A theoretical study

Motivated by the captivating allure of exquisitely regulated characteristics exhibited by 2-(2-hydroxyphenyl)-benzoxazole and its derivatives in the domains of photochemistry and photophysics, our current endeavor primarily focuses on delving into the intricacies of photo-induced excited state reactions for derivatives of 2,5-bis(benzoxazol-2-yl)-thiophene-3,4-diol (BTD). Given the profound impact of chalcogen element doping, our primary focus lies in investigating the excited state behaviors of BTD-O, BTD-S, and BTD-Se fluorophores. Through simulations encompassing variations in geometry and vertical excitation charge reorganization, we unveil atomic-electronegativity-dependent hydrogen bonding interactions and photoexcitation-induced charge recombination that can significantly augment the intramolecular double proton transfer (ESDPT) reaction in the excited state for BTD-O, BTD-S, and BTD-Se fluorophores. By constructing potential energy surfaces and identifying transition state forms, we elucidate the ultrafast stepwise ESDPT mechanism facilitated by the low potential barriers. Moreover, we rigorously validate the chalcogen atomic electronegativity-driven regulation of the stepwise ESDPT mechanism. We sincerely anticipate that manipulating solvent polarity will pave the way for groundbreaking advancements in luminescent materials.