Network reaction of 2,6-bis(2-hydroxybenzilidene)cyclohexanone by external stimuli

The pH-dependent photochromic behaviour of a curcumin analogue, 2,6-bis(2-hydroxybenzilidene)cyclohexanone (HBC) has been investigated. The identification of stable and unstable species from network reaction was done by combination of NMR, UV–vis and fluorescence spectroscopy. The structure of stable species was established by 13C NMR, 1H NMR and 2D NMR spectra: DQF-COSY, HSQC and HMBC. The results indicate that HBC could be used as pH sensor on a 1–5 scale. Experimental results were correlated by theoretical calculations using ZINDO/S/CI semi-empirical methods. HBC exhibits fluorescent properties both in acidic and neutral media and in basic environment the fluorescence is quenched.