Investigation of ESIPT in a panel of chromophores presenting N-H⋯N intramolecular hydrogen bonds

Thermodynamic and kinetic aspects of excited state intramolecular proton transfer (ESIPT) are investigated in 11 chromophores harboring an intramolecular N-H⋯N hydrogen bond [pyridyl pyrazole, pyridyl pyrrole, azaindole, pyridyl indole, pyrroloquinoline, and an analogue of the Blue Fluorescent Protein (BFP) chromophore] with the help of quantum mechanical calculations. For pyridyl pyrazoles, simulated spectra are used to help the interpretation of experimental ones and the effects of several substituents are investigated. Then it is shown that Time-Dependent Density Functional Theory fails to satisfactorily describe the energetic aspects of ESIPT for the BFP chromophore analogue. Equation-of-Motion Coupled Cluster theory is thus used to reach accurate insights for this challenging case. This journal is