Structure–property relationships in para-substituted nitrobenzofurazans: electrochemical, optical, and theoretical analysis

In this work, we seek to understand and to quantify the structure–property relationships of chlorine, methoxy and phenoxy para-substituted nitrobenzofurazans (NBDs). Optical and electrochemical properties of studied materials were explored using UV–Vis spectroscopy and cyclic voltammetry (CV), respectively. Through an extrapolation of the linear trend observed in the UV–Vis spectra, the estimated energy band gaps for chlorine, methoxy and phenoxy para-substituted nitrobenzofurazans (NBDs) are 3.22, 2.89 and 2.94 eV, respectively. The electrochemical energy gaps deduced from the CV measurements are 3.34 eV (NBD-Cl), 3.00 eV (NBD-OCH 3 ) and 3.01 eV (NBD-OC 6 H 5 ). The almost complete agreement between the values determined by the two independent experimental methods is remarkable. In addition, the DFT computed band gap energies are closer to the experimental values. Further, the DFT and its extension of TD-DFT methods combined with several topological analyses have been used to understand the nature and the intra-molecular charge transfer (ICT) abilities within the studied molecules.