Investigations on the photochromic properties of 2,6-bis(5-bromo-2-hydroxybenzylidene)cyclohexanone.

The network of chemical reactions of 2,6-bis(5-bromo-2-hydroxybenzylidene)cyclohexanone (BHBC) when subjected to light and different pH values has been investigated. The pH dependent species involved in the chemical network have been identified and characterized by NMR and UV-VIS spectroscopy. Direct pH jumps were carried out by adding a strong acid to equilibrated solutions of trans-chalcone (Ct) forming the flavylium cation which was stable only under extremely acidic conditions (pH < 0.5). The single crystal X-ray study and NMR analysis has confirmed the structure of the new flavylium cation. In the case of a reverse pH jump, the Ct species interconverted instantaneously into deprotonated trans-chalcone (Ct