Study of the photochemical properties and conical intersections of [2,2'-bipyridyl]-3-amine-3'-ol

The two isoelectronic bipyridyl derivatives [2,2'-bipyridyl]-3,3'-diamine and [2,2'-bipyridyl]-3,3'-diol are experimentally known to undergo very different excited-state double-proton-transfer processes, which result in fluorescence quantum yields that differ by four orders of magnitude. In a previous study, these differences were explained from a theoretical point of view, because of topographical features in the potential energy surface and the presence of conical intersections (CIs). Here, we analyze the photo-chemical properties of a new molecule, [2,2'-bipyridyl]-3-amine-3'-ol [BP(OH)(NH2)], which is, in fact, a hybrid of the former two. Our density functional theory (DFT), time-dependent DFT (TDDFT), and complete active space self-consistent field (CASSCF) calculations indicate that the double-proton-transfer process in the ground and first singlet pi ->pi* excited state in BP(OH)(NH2) presents features that are between those of their "parents'. The presence of two CIs and the role they may play in the actual photochemistry of BP(OH)(NH2) and other bipyridyl derivatives are also discussed.