Thermogravimetric and differential thermal analyses of fluorescein dye in inert and static air atmosphere

Fluorescein dye was prepared and characterized on the basis of microanalytical methods, FTIR, NMR and UV–visible spectroscopy in order to ensure its purity. Thermoanalytical study by TG, DTA and DTG was conducted in air as well as in inert atmosphere to determine the mode of decomposition and stability. The dye follows two-step and three-step decomposition pattern in air and nitrogen, respectively. The first stage of decomposition in both environments yields carbon monoxide and oxygen, whereas carbon monoxide and acetylene are the common products of second-stage decomposition except anthracene which is released only in air. The third step evolves ketene and acetylene under inert condition and the residue (observed at 1133 K) is a highly conjugated cyclic system. Char is the only residue which is identified at the end of decomposition under air after 893 K. The intermediates formed during the decomposition processes were also investigated. A possible mechanism of the thermal decomposition is proposed depending on pyrolysis, MS and IR spectral data.