To what extent are the photophysical properties of quinoxaline- and quinoxalinone-based chromophores predictable?

Abstract

A series of chromophores containing quinoxaline or quinoxalinone electron-acceptor (A) and dialkylaminostyryl electron-donor (D) units linked by π electronic bridge has been synthesized. Electronic emission and absorption spectra of the novel D-π-A, D-π-A-π-D or D-π-A-π-A-π-D systems cover a broad range from ultraviolet to near infrared. Positions and relative intensities of their absorption bands are shown to depend strongly on structural modifications of the molecules, while emission in solution strongly depends on both the structure of the solute and the solvent polarity. Quantum chemical modeling provided a reliable description of the observed absorption spectra and reproduced the positions of the emission bands. Quantum yields of emission are shown to be qualitatively predictable on the basis of empirical rules connecting the luminescence intensity with the chemical structures of both quinoxaline- and quinoxalinone-based luminopohores and the polarity of the solvents used. Theoretical assessment of the character of the main electronic transitions suggests that simultaneous presence of D and A units conjugated via π-bridges ensures the intramolecular charge-transfer effects probably underlying the observed similar solvatochromism for all the studied systems irrespective of their polarity.