Theoretical investigation on electronic, optical, and charge transport properties of 7,8,15,16-tetraazaterrylene and its derivatives with electron-attracting substituents

Electronic, optical, and charge transport properties of 7,8,15,16-tetraazaterrylene (TAT) and its three tetrasubstituted derivatives with the electron-attracting substituent have been studied theoretically using density functional theory (DFT) calculations coupled with the incoherent charge-hopping model. The calculated results reveal that the introduction of electron-attracting substituents, which does not break down the planar skeleton of TAT core, can stabilize the extended π-system and then improve the electron injection efficiency as well as the ambient stability. Based on TAT single-crystal structure, the predicted 3D-average electron mobility reaches as high as 3.404 × 10−2 cm2 V−1 s−1 at 300 K, but the hole mobility is only 6.516 × 10−4 cm2 V−1 s−1, which indicates that TAT single crystal may be a promising candidate as n-channel materials. The simulation of the angle-resolved electron mobility shows that TAT single-crystal possesses a remarkably anisotropic electron-conducting behaviour, and the maximum electron mobility is found to be along the crystallographic a-axis direction. In addition, the calculated reorganization energies and electronic coupling values show that the three TAT derivates (4F-TAT, 4Cl-TAT, and 4CN-TAT) designed in this work may well be potential n-channel materials with the high electron mobility. TD-DFT B3LYP/6-311G(d,p) calculations reveal the most relevant electronic transitions for the studied compounds present the π → π* character and the strongest absorption and emission peaks are dominated by the transitions of HOMO → LUMO. The introduction of electron-withdrawing substituents red-shifts the maximal absorption and emission wavelengths.