Theoretical Investigations on Charge-Transfer Properties of Novel High Mobility n-Channel Organic Semiconductors - Diazapentacene Derivatives

The charge-transfer properties of three diazapentacene derivatives, including 5,7,12,14-tetrachloro-6,13-diazapentacene (TCDAP), 5,7,12,14-tetrachloro-6,13-diaza-6,13-dihydropentacene (TCDAHP), and 5,7,12,14-tetrafluoro-6,13-diazapentacene (TFDAP), have been studied using density functional theory. The performance of five pure GGA and seven hybrid GGA functionals and G3MP2B3 method on the reorganization energy (lambda) and mobility (mu) predictions of TCDAP has been examined. Both the B3LYP functional and the G3MP2B3 method give reliable predictions for the lambda value. Using the reorganization energy at the G3MP2B3 level together with the transfer integral by BHandH, BHandHLYP, and M06-2X functionals yields electron mobilities of 3.44, 3.32, and 3.29 cm(2) V-1 S-1 for TCDAP, respectively, which come fortuitously close to the experimental value of 3.39 cm(2) V-1 S-1. Other density functionals also give mobility predictions in agreement with the experimental value to a factor of similar to 2. The TCDAHP, a -NH derivative of TCDAP, is predicted to have a large hole and electron mobility of 2.30 and 3.89 cm(2) V-1 S-1, respectively. Our results suggest that TCDAP is an n-channel material, while TCDAHP is an ambipolar organic semiconductor with simultaneous hole and electron transport properties. By the substitution of chlorine with fluorine in TCDAP, we find that TFDAP is very similar to TCDAP in terms of the molecular and crystal structure and HOMO/LUMO property. TFDAP is an n-type semiconductor but with a larger electron mobility of 3.51 cm(2) V-1 S-1. All theoretical predictions are based on the crystal structures obtained with PBC model and B97D functional. The transfer integral calculations along the four dominant hopping pathways reveal that the hole and electron transport processes occur via the parallel routes between two neighboring molecules with pi-stacking interactions. On the basis of the angular resolution anisotropic mobility analyses, TCDAP, TCDAHP, and TFDAP show remarkably different anisotropic behaviors in comparison with the 6,13-dihydro-6,13-diazapentacene (DHDAP).