Pressure-driven neutral-ionic transition in ClMePD-DMeDCNQI - art. no. 144102

Application of about 0.8 GPa pressure is sufficient to induce the neutral-i onic transition in the mixed stack charge-transfer crystal 2-chloro-5-methy l-p-phenylenediamine-2,5-dimethyl-dicyanoquinonediimine (CIMePD-DMeDCNQI). The ionicity increases continuously from similar to0.35 at ambient conditio ns to similar to0.65 when the pressure is raised up to 2 GPa. Moreover, sta ck dimerization begins well before the crossing of the neutral-ionic interf ace. The evolution of the transition is similar to what observed in the tem perature-induced phase change in the same compound. A distinguishing featur e is represented by the simultaneous presence of domains of molecules with slightly different ionicities across the transition pressure. A comparison of the present example of a pressure-driven neutral-ionic transition with t he well-studied cases of tetrathiafulvalene-chloranil and of tetrathiafulva lene-2,5-dichloro-p-benzoquinone puts in evidence the remarkably different evolution of the three transitions.