Dipolar Properties of and Temperature Effects on the Electronic States of 3-Hydroxyflavone (3HF) Determined using Stark-Effect Spectroscopy and Compared to Electronic Structure Calculations

3-Hydroxyflavone (3HF) is a molecule that undergoes excited-state intramolecular proton transfer (ESIPT). Using electroabsorption we have detected the small changes in dipole moment (|∆μ b|) and polarizability (∆R) resulting from photon absorption for 3HF embedded in a noninteracting polyethylene environment. The values of |∆μ b| and ∆R obtained are also in good agreement with the results of ab initio 6-31G(2d,p) calculations but not with those obtained using INDO1/s. The electroabsorption spectra at 298 and at 77 K contain contributions from at least two overlapping electronic transitions within the wavelength region being probed. Two methods are discussed for extracting the electronic dipolar properties from these spectra that produce consistent results for the transition responsible for ESIPT. Interestingly, the relative intensities of the electroabsorption signals arising from the two electronic transitions studied here are observed to vary with temperature. The intensity change seen in the higher energy transition may be attributed to contributions from transition moment polarizability and hyperpolarizability components.