Charge Transport in Structurally Related Organic Semiconductors: Experimental Determination and Computational Modeling in Crystalline and Amorphous Scenarios

Herein, the charge transport properties of two organic semiconductors (1 and 2) with tiny differences in the π-conjugated scaffold but distinct crystal arrangements are thoroughly rationalized by a combined experimental and computational characterization. Compound 1, including 7-azaindole units in the π-conjugated core, is designed to promote intermolecular hydrogen bonding and induce certain order in the solid-state structure with multiple face-to-face π–π interactions. In contrast, compound 2, for which the terminal pyridine rings of the 7-azaindole units are substituted by phenyl rings, thus precluding the formation of intermolecular hydrogen bonds, exhibits the typical herringbone crystal arrangement of acenes. The alkyl chains end-capping the conjugated cores also play a noticeable effect on the molecular arrangement. These structural features determine the performance of the organic semiconductors in organic field-effect transistors (OFETs), with 2 showing a better hole mobility. The computational strategy used to study the charge transport properties sheds light onto the behavior of both compounds, and predicts higher hole mobilities for 2 compared to 1 both in crystal and amorphous phases in line with the experimental measurements. While the origin of the enhanced carrier mobility displayed by 2 in the crystal results from the better intermolecular electronic coupling between adjacent molecules, its higher mobility in the amorphous phase seems to arise from the smaller internal reorganization energy computed for 2 compared to 1.