NMR study of proton dynamics in the NHO hydrogen bonds in the thermochromic crystals of N-salicylideneanilines

Abstract

The precise investigation of the spin—lattice relaxation rate of the proton of the remarkably thermochromic crystal of N,N′-bis(salicylidene)- p-phenylenediamine provides unique information of proton dynamics in the NHO hydrogen bonds, which is consistent with the temperature dependence of the visible absorption spectra of this crystal and which reveals the presence of interaction between two NHO hydrogen bonds in the molecule through rearrangement of the configuration of π-electrons. This result indicates that the thermochromism of this material is a prototype of “proton—electron cooperation”. The transfer rate of proton in the NHO hydrogen bond is strongly affected by a chemical modification, e.g. the fast tunneling.