Temperature-induced neutral-ionic transition in dimethyltetrathiafulvalene-p-chloranil

A new 1:1 mixed-stack organic charge-transfer crystal of 2,6-dimethyltetrathiafulvalene-p-chloranil (DMTTF-CA), which undergoes a temperature-induced neutral-ionic transition (TINIT), was reported. At a critical temperature of 65±{}5 K the molecular ionicity and the stack dimerization were found to change discontinuously. A most striking feature in the phase transition of DMTTF-CA was that a neutral-ionic coexisting phase did appear at lower temperatures, unlike the homogeneous ionic phase observed for the TINIT of tetrathiafulvalene-p-chloranil (TTF-CA). These transition characteristics were discussed by taking into account the structural differences between these two complexes composed of similar constituents.