J. Phys. IV France 12 (2002) Pr9-357
DOI: 10.1051/jp4:20020437

One-dimensionality and neutral-to-ionic transition of some mixed-stack charge-transfer complexes

M. Buron¹, E. Collet¹, M.H. Lemée-Cailleau¹, H. Cailleau¹, T. Luty^{1, 2}, S. Ravy³ and J.F. Bérar<sup>4

1</sup>  Groupe Matière Condensée et Matériaux, CNRS, Université de Rennes 1, 35042 Rennes, France
²  Institute of Physical and Theoretical Chemistry, Technical University, 50370 Wroclaw, Poland
³  Laboratoire de Physique des Solides, CNRS, Université Paris-Sud, 91405 Orsay, France
⁴  D2AM-CRG/ESRF & Laboratoire de Cristallographie, CNRS, 38042 Grenoble, France

Abstract
Mixed-stack charge-transfer (CT) complexes undergoing the neutral-ionic (N-I) phase transition are molecular materials formed of stacks where electron donor (D) and acceptor (A) molecules regularly alternate. In the N phase, the CT is low and molecules are situated on inversion centers, while in the I phase, the increase of CT is accompanied by a lattice distortion (dimerization process and symmetry breaking). The one-dimensional (1D) architecture triggers the chain multistability by stabilizing lattice-relaxed (LR)-CT excitations ...D° A° D° A° (D⁺A^-)(D⁺A^-)(D⁺A^-) Do A" D° A° D°... These 1D nano-scale objects are at the heart of the equilibrium N-I phase transition and govern the fascinating physical properties such as giant dielectric response or photo-induced phase transformations. In this contribution, the 1D character of these critical excitations will be demonstrated by direct observation using high resolution X-Ray diffraction.

© EDP Sciences 2002