Regulated stepwise ESDPT mechanism associated with chalcogen substitutions in BDIBD derivatives

state, which is favorable for the occurrence of ESPT reactions. The charge recombination behavior of hydrogen bonds, induced by photoexcitation, further illustrates this point. By constructing potential energy surfaces (PESs) based on restrictive optimization and by searching the transition state (TS) structure, we finally elucidate stepwise excited-state double proton transfer (ESDPT). Specifically, we confirm that a change in atomic electronegativity has a regulatory effect on the ESDPT behavior in BDIBD derivatives, that is, lower atomic electronegativity is more conducive to stepwise ESDPT.