Theoretical design of a hole-transporting molecule: hexaaza[16]parabiphenylophane

Abstract

We theoretically propose a hole-transporting molecule, hexaaza[1₆]parabiphenylophane (HAPBP), on the basis of vibronic coupling density (VCD). We calculate vibronic coupling constants (VCCs) of HAPBP and compare them with those of other well-known hole-transporting materials, N,N′-bis(3-methylphenyl)-N,N′-diphenyl[1,1′-biphenyl]-4,4′-diamine (TPD), N,N,N′,N′-tetraphenylbenzidine (TAD), and N,N′-di(1-naphthyl)-N,N′-diphenyl[1,1′-biphenyl]-4,4′-diamine (α-NPD). HAPBP has smaller VCCs than TPD, TAD, and α-NPD. Employing VCD analysis, we reveal the reason for the small VCCs of HAPBP. To investigate their single molecular hole-transporting properties, we calculate current–voltage characteristics and power loss using the non-equilibrium Green's function (NEGF) method taking into account inelastic scatterings due to the vibronic couplings. HAPBP, because of its small VCCs, exhibits more efficient hole-transporting properties and lower power loss than TPD, TAD, and α-NPD. Furthermore, as a hole-transporting material, HAPBP has more suitable highest occupied and lowest unoccupied molecular orbital energies than TPD, TAD, and α-NPD. HAPBP is a promising candidate for a hole-transporting material in organic light-emitting diodes (OLEDs).