Turning ESIPT-Based triazine fluorophores into dual emitters: From theory to experiment

In an effort to design new dyes presenting multiple fluorescence bands, we use theoretical chemistry to guide the synthesis of new triazine structures undergoing excited-state intramolecular proton transfer (ESIPT). Starting with experimentally-known compounds showing emission from the keto tautomer only, we model several chemically-achievable substitutions aiming to sufficiently frustrate the ESIPT process by stabilising the enol structure in the electronic excited state. In a second step, some of the proposed dyes are synthesised. It turns out that the emergence of an emission band due to the enol confirms the theoretical prediction, though the observed quantum yields in solution are small most probably due to the selection of methoxy substituents. The quantum yields are strongly improved when going to the solid-state as a result of the impeded rotations