Excited state intermolecular proton and energy transfer of 1-hydroxypyrene interacting with the human serum albumin protein

► 1-Hydroxypyrene forms robust 1:1 complexes with HSA protein at binding site I. ► No excited state intermolecular proton transfer in aqueous phosphate buffer (pH 7). ► Excited state intermolecular proton transfer to amino acid residue proceeds in ∼400 ps. ► Energy transfer with 77% efficiency from excited Trp214 to encapsulated 1-hydroxypyrene is reported.