Effect of Nitrogen Doping and Acene Cores Elongation on Charge Transport and Electronic Nature of Organic Semiconductor Materials: A DFT Study

With the intention to tune the charge transport nature of preliminary 4,6-di(thiophen-2-yl)pyrimidine (DTP) structure, six novel V-shaped organic semiconductor compounds were designed by nitrogen doping and acene moieties elongation. Initially, the nitrogen atoms were doped in DTP to design 4,6-bis-thiazol-2-yl-pyrimidine (1). Moreover, by ℼ-bridge elongation strategy, 4,6-bis-benzo[b]thiazol-2-yl-pyrimidine (2), 4,6-bis(naphthothiazol-2-yl)pyrimidine (3), 4,6-bis(anthracenothiazol-2-yl)pyrimidine (4), 4,6-bis(tetracenothiazol-2-yl)pyrimidine (5), and 4,6-bis(pentacenothiazol-2-yl)pyrimidine (6) were designed by substituting various oligocenes at both ends. The ground, as well as excited state structures, were optimized using density functional theory (DFT) and time-dependent DFT at B3LYP/6-31G** and TD-B3LYP/6-31G** levels, correspondingly. We explored their frontier molecular orbitals, electron injection aptitude, photo-stability, Ionization Energies (IE), electron affinity (EA), and reorganization energies. The bridge elongation significantly elevates the EA while reducing the IE which would result in to decrease in the injection barrier for electron and hole transport. Furthermore, acene cores elongation expressively decreases the hole and electron reorganization energies as compared to frequently used materials pentacene and tris(8-hydroxyquinolinato)aluminum (mer-Alq3) which revealed that newly designed materials would be proficient to be used in p- and/or n-type semiconductor devices.