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 S ₁ state, estimated to be smaller than that in the S ₀ state, suggests that the geometry of HPBI is substantially twisted in the S ₁ state.