New NIR dyes for ammonia sensing

Three series of new cyanine dyes were synthesised and the Vis–NIR spectra of the dyes were measured and interpreted by semi-empirical methods of quantum chemistry. As a basic building block for the synthesis, 4-(dimethylaminomethylene)-5-oxo-2-furfurylidenedimethyliminium perchlorate I was used. The dyes were prepared by condensing I with appropriate salts. The tests for sensitivity to ammonia have shown that the series of mono-substituted dyes III are reversibly sensitive to ammonia in ethanol solutions. The dyes exhibit a peak at 620–680 nm arising from the interaction with ammonia and, hence, these dyes are promising as chemical transducers for distributed fibre-optic ammonia sensors.