Non-merohedrally twinned crystals of N,N′-bis(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine:: an excellent triphenylarnine-based hole transporter

N,N'-Bis(3-methylphenyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine(TPD), C38H32N2, crystallizes in the monoclinic space group P2(1) with a pseudo-orthogonal lattice, rather than the previously reported orthorhombic space group P2(1)2(1)2(1) [Kennedy, Smith, Tackley, David, Shankland, Brown & Teat (2002). J. Mater. Chem. 12, 168-172]. The asymmetric unit consists of two independent molecules, A and B, which are arranged along the [100] direction to form vertical layers of alternately stacked A and B molecules. Molecule A shows a great deal of rotational movement in the four terminal aryl rings, resulting in two disordered tolyl groups split over two sites, while molecule B exhibits an almost cis configuration of the two terminal tolyl groups with respect to these ring planes.