Nodal-plane model for excited-state intramolecular proton transfer of o-hydroxybenzaldehyde: substituent effect

The excited-state intramolecular proton transfer (ESIPT) of o-hydroxybenzaldehyde (OHBA) and related molecules in solution has been studied by emission spectroscopy. The substituent effects on the fluorescence quantum yield for the lowest excited 1(π,π∗) state can be explained by considering the nodal pattern of the wave function along with the delocalization of the π electrons in the excited state. The substituent effect in 5-substituted salicylaldehydes is much less than that in o-(substituted-formyl)phenols.