Changes in the electric dipole moments and molecular polarizabilities of enol and keto forms of 2-(2′-hydroxyphenyl)benzimidazole along the proton transfer reaction path in a PMMA film

Electroabsorption and electrophotoluminescence spectra were investigated for 2-(2′-hydroxyphenyl)benzimidazole in PMMA, and the results were compared with quantum chemical calculations. The electroabsorption spectrum of the enol form was ascribed to a change in the molecular polarizability following photoexcitation. On the other hand, the electrophotoluminescence spectrum of the keto form was interpreted as a difference in the electric dipole moment between the excited and ground states. The molecular polarizability of the keto form in the S1 state, estimated to be smaller than that in the S0 state, suggests that the geometry of HPBI is substantially twisted in the S1 state.