Design of quantum neutral–ionic phase transition in organic charge-transfer complexes

Neutral–ionic (NI) phase transition has been investigated by various chemical modifications in the prototype complexes of TTF (or DMTTF)-p-chloranil. Successive lattice expansion due to the enlarged molecular size serves to lower the NI transition temperature. From the dielectric properties and the molecular ionicity, we demonstrate the novel examples of the NI transition, which is affected by the quantum fluctuation effect.