Structural effects on the vibrational behaviour of N,N '-diphenyl-1,4-phenylenediamine

A vibrational study of two crystalline forms of the N,N-diphenyl-1,4-phenyl enediamine molecule is reported. This compound shows polymorphism in its so lid state, i.e. either an orthorhombic or a triclinic structure is obtained depending on the conditions of crystallization. Three conformational isome rs are evidenced in these structures, showing significant differences betwe en their geometric parameters, especially their torsional angles. These obs ervations are also supported by the vibrational features characteristic of the conformers in the crystals. Several changes are observed in the infrare d absorption (ir) and Raman scattering data. This work concerns mainly the polarized Raman measurements on these two crystalline forms. A detailed ana lysis and a good knowledge of phenyl compounds allow a very precise assignm ent of the vibrational modes and also reveals the structure-properties (esp ecially molecular conformations-vibrational properties) relationships in th ese systems. In particular, the effect of the crystalline arrangement and o f the local symmetry between neighbouring molecules is discussed. Copyright (C) 2001 John Wiley & Sons, Ltd.