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

► External electric field effects on the electronic spectra are investigated. ► The electric dipole moment and molecular polarizability depend on the tautomer. ► The geometry of the keto form in S1 is substantially twisted.