The enhanced ultrafast dissociation of meso-hydrogen of bis(indolyl)methane derivatives under acidic conditions

Abstract

Bis(indolyl)methane (BIM) derivatives are an important class of molecules that have shown vivid applications. The photo dynamics of BIM derivatives has been studied through ultrafast spectroscopy. It has been observed that the acidic medium plays a vital role in governing the spectral characteristics of BIMs, imputing to the ambivalent nature of BIMs under acidic conditions. We noticed that the dissociation of meso-hydrogen is enhanced under acidic conditions, while no such enhancement is observed under alkaline and neutral conditions. We further perceived that the dissociation of meso-hydrogen takes precedence over the dissociation of N–H bonds, even in an acidic medium. Quantum chemical calculations support the experimental observations. Although the functionalisation with electron-withdrawing or electron-donating groups seems to affect photophysical properties such as spectral shift, quantum yield, etc., tuning the acidic medium plays a significant role.