Theoretical Insights into Excited-State Stepwise Double Proton Transfer Associated with Solvent Polarity for 2-bis(benzothia-zolyl)naphthalene-Diol Compound

Inspired by the excellent photochemical properties of 2-(2 & PRIME;-hydroxyphenyl)benzazole and its derivatives, in this work, the novel 2-bis(benzothia-zolyl)naphthalene-diol (2-BBTND) fluorophore is explored about its photo-induced behaviors. The intramolecular double hydrogen bonding interaction and the excited state intramolecular double proton transfer (ESDPT) behavior of 2-BBTND fluorophore are investigated in combination with different polar solvent environments. From the structural changes and charge recombination induced by photoexcitation, we can affirm that strong polar solvent environment promotes the excited state dynamical reaction for 2-BBTND compound. By constructing potential energy surfaces (PESs) in S-0 and S-1 states, we clarify that 2-BBTND fluorophore should undergo the stepwise ESDPT reaction after photoexcitation. Combined with the size of potential energy barriers along with reaction paths in different solvents, we finally propose a new solvent-polarity-dependent stepwise ESDPT for 2-BBTND fluorophore.