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

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.