Application of a carbazole derivative as a spectroscopic fluorescent probe for real time monitoring of cationic photopolymerization

The performance of 1-(9-ethylcarbazol-3-yl)-4,4,4-trifluorobutane-1,3-dione (1) as a fluorescent probe for the monitoring of cationic photopolymerization processes by Fluorescence Probe Technique (FPT) has been evaluated in comparison with the response of 7-diethylamino-4-methylcoumarin (Coumarin 1) (2). Triethylene glycol divinyl ether and diphenyliodonium hexafluorophosphate were used as an example monomer and a cationic photoinitiator respectively. It has been found that the probe 1 withstands the cationic polymerization conditions and provides correct probe response. 1-(9-ethylcarbazol-3-yl)-4,4,4-trifluorobutane-1,3-dione shifts its fluorescence spectrum with progress of cationic photopolymerization of the monomer, which enables the monitoring of the polymerization progress using the fluorescence intensity ratio measured at two different wavelengths as the progress indicator. By comparing the behavior of 1 and 2, it has been documented that the fluorescence spectrum of probe 1 shows a spectacular hypsochromic shift (Δλ = 33 nm) upon the monomer polymerization, while the shift of 2 is three times smaller (Δλ = 11 nm). Moreover, the sensitivity of probe 1 is more than 2.5-times higher than that of any other probes suitable for monitoring cationic polymerization processes, reported previously. Therefore, application of the carbazole derivative (1) as a new probe for the monitoring of the crosslinking process of coatings cured by cationic photopolymerization has been proposed.