Push-pull effect on the charge transport characteristics in V-shaped organic semiconductor materials

With the goal to tune charge transport and electronic properties of 4,6-di(thiophen-2-yl)pyrimidine (DTP) structure, seven novel V-shaped organic semiconductor compounds were designed by nitrogen doping, oligocenes π-bridge incorporations and push-pull strategy. Primarily, 4,6-bis-thiazol-2-yl-pyrimidine (1) was designed by nitrogen atoms doping in DTP. Then push-pull system named 1DA was designed by substituting –N(CH3)2 at R1 and R2, while –CF3 at R3 and R4 positions of 1. Moreover, various semiconducting materials (2DA-6DA) with tuned properties were designed from 1DA by fusing benzene, naphthalene, anthracene, tetracene and pentacene at both ends. The density functional theory (DFT) and time-dependent DFT were adopted for optimizing the ground and excited state structures, correspondingly. We investigated frontier molecular orbitals, photo-stability, electron injection, electron affinity (EA), ionization energies (IE) and reorganization energies. The push-pull and π-bridge elongation strategies ominously raise EA while diminish IE values, which may lead to decrease the electron and hole injection obstruction. Besides, donors–acceptors and oligocenes at both ends meaningfully drop the electron reorganization energy values as compared to normally used n-type material, i.e., tris(8-hydroxyquinolinato)aluminium (mer-Alq3). These results revealed that newly designed materials 4DA-6DA would be proficient to be used in n-type semiconductor devices.