Experimental and Theoretical Exploration of Aryl Substituent Effects on the Electronic Properties of Asymmetric 4,7-Di(thiophene-2-yl)-benzo[c][2,1,5]thiadiazole Compounds

By introducing phenyl, 1-naphtyl, 2-thienyl, 2-furanyl and 3-pyridyl rings into 4,7-di(thiophene-2-yl)-benzo[c][2,1,5]thiadiazole structure 2, five new asymmetric derivatives were prepared. For these compounds, HOMO/LUMO and gap energy levels were estimated by UV-Vis and cyclic voltammetry experiments in aprotic solvents. The results showed significant effects of aryl groups on gap data, were this parameter was mainly tuned by changes in the HOMO level of structure 2. These properties were examined also by electronic structure calculations and the estimations obtained described the experimental trends. Quantum chemical modeling exhibited homogeneous distribution of HOMO and LUMO energy levels in all studied compounds and suggest that planarity in the system is crucial to diminish the gap. The calculations also explain that, a conformational change (predicting a 54.2 degrees dihedral angle between the 1-naphtyl substituent and the rest of the molecule) was responsible for the unexpected increase in gap of compound bearing a 1-naphtyl substituent; the latter phenomenon was corroborated by X-Ray information, which reveals a dihedral angle of 46.8 degrees.