Switching between cisand transanions of 2-(2'-hydroxyphenyl)benzimidazole: a molecular rotation perturbed by chemical stabilization

Despite the fact that 2-(2'-hydroxyphenyl)benzimidazole (HPBI) exists as the cisand transenol in neutral form, it was reported to exist only in the transform upon deprotonation in an aqueous medium. It was also shown that the dianion formed in the ground state can be re-protonated to form the trans-anion in the excited state. In the present study, the cis-anion and dianion could be obtained upon proper stabilization in suitable environments. Switching between the cisand trans-anion was demonstrated to be possible by changing the environment. Theoretical calculations were performed to substantiate the existence of the cis-anion and dianion. In contrast to a literature report, it was shown that the 'OH' group deprotonates before the 'NH' group to form a monoanion not only in protic solvents but also in aprotic solvents.