Studies on the synthesis and thermochromic properties of crystal violet lactone and its reversible thermochromic complexes

In this article, a crucial compound, crystal violet lactone (CVL), was prepared by the reaction of NN-dimethylaniline, p-dimethylanimobenzaldehyde and m-dimethylanimobenzoic acid. Taking alcohols or carboxylic acids as solvents, 15 novel reversible thermochromic complexes were prepared by means of chelation reaction between electron donor CVL and electron acceptor such as various phenols, aromatic amines, carboxylic acids, and Lewis acids, respectively. The structure of CVL is characterized by H-1 NMR and MS. The reversible thermochromic behavior of these compounds are studied by DSC/TG, IR, and Raman spectrum. Results indicate that mechanism of these reversible thermochromic complexes is the lactone ring tautomerism when the temperature is low or high. Thermochromic color degree of these complexes is dependent on the acidity of electron acceptor and thermochromic temperature is dependent on the properties of solvent compounds. The properties of electron acceptor and solvent compounds also determined the thermochromic process of the complexes, which followed the first-order kinetic equation, and the values of energy of activity (Ea) of thermochromic process are correlated with the components of the complexes nearly. The stronger the acidity of phenols is, and the deeper the thermochromic color degree is, the higher the value of Ea is, when electron acceptors are phenols. (C) 2003 Elsevier B.V. All rights reserved.