Tuning the energy level of TAPC: crystal structure and photophysical and electrochemical properties of 4,4′-(cyclohexane-1,1-diyl)bis[N,N-bis(4-methoxyphenyl)aniline]

Abstract

The energy level of a hole-transporting material (HTM) in organic electronics, such as organic light-emitting diodes (OLEDs) and perovskite solar cells (PSCs), is important for device efficiency. In this regard, we prepared 4,4′-(cyclohexane-1,1-diyl)bis[N,N-bis(4-methoxyphenyl)aniline] (TAPC-OMe), C46H46N2O4, to tune the energy level of 4,4′-(cyclohexane-1,1-diyl)bis[N,N-bis(4-methylphenyl)aniline] (TAPC), which is a well-known HTM commonly used in OLED applications. A systematic characterization of TAPC-OMe, including 1H and 13C NMR, elemental analysis, UV–Vis absorption, fluorescence emission, density functional theory (DFT) calculations and single-crystal X-ray diffraction, was performed. TAPC-OMe crystallized in the triclinic space group P\overline{1}, with two molecules in the asymmetric unit. The dihedral angles between the central amine triangular planes and those of the phenyl groups varied from 26.56 (9) to 60.34 (8)° due to the steric hindrance of the central cyclohexyl ring. This arrangement might be induced by weak hydrogen bonds and C—H...π(Ph) interactions in the extended structure. The emission maxima of TAPC-OMe showed a significant bathochomic shift compared to that of TAPC. A strong dependency of the oxidation potentials on the nature of the electron-donating ability of substituents was confirmed by comparing oxidation potentials with known Hammett parameters (σ).