Halogenated Tetraazapentacenes with Electron Mobility as High as 27.8 cm2 V-1 s-1 in Solution-Processed n-Channel Organic Thin-Film Transistors.

Molecular engineering of tetraazapentacene with different numbers of fluorine and chlorine substituents fine-tunes the frontier molecular orbitals, molecular vibrations, and π-π stacking for n-type organic semiconductors. Among the six halogenated tetraazapentacenes studied herein, the tetrachloro derivative (4Cl-TAP) in solution-processed thin-film transistors exhibits electron mobility of 14.9 ± 4.9 cm2 V-1 s-1 with a maximum value of 27.8 cm2 V-1 s-1 , which sets a new record for n-channel organic field-effect transistors. Computational studies on the basis of crystal structures shed light on the structure-property relationships for organic semiconductors. First, chlorine substituents slightly decrease the reorganization energy of the tetraazapentacene whereas fluorine substituents increase the reorganization energy as a result of fine-tuning molecular vibrations. Second, the electron transfer integral is very sensitive to subtle changes in the 2D π-stacking with brickwork arrangement. The unprecedentedly high electron mobility of 4Cl-TAP is attributed to the reduced reorganization energy and enhanced electron transfer integral as a result of modification of tetraazapentacene with four chlorine substituents.