Stimuli-responsive emission of quinoxalinone-based compounds. From experimental findings to theoretical insight by means of multiscale computational spectroscopy approaches

Abstract

The drastic differences in absorption spectra of structurally close quinoxalinone derivatives, containing electron-donor and -acceptor units, are rationalized, by means of theoretical tools. They are ascribed to the difference in the intramolecular charge-transfer character of the electronic transition corresponding to the experimental longest-wavelength absorption bands of these systems. Charge-transfer compounds are not luminescent in solutions, in contrast to their analogs with weaker charge-separation and longer π-conjugated backbone, which suggests that the main factor “switching-off” emission is related to their “push-pull” properties and the balance between the length of the π-conjugated backbone and the donor-acceptor strength. Furthermore, the protonation of the studied quinoxalinones is shown to result in a weakening of the donor-acceptor strengths and conjugation efficiency, thus limiting charge-transfer and producing the emission response in the acidified solutions.