Photosensitization of carbazole derivatives in cationic polymerization with a novel sensitivity to near‐UV light

Abstract

Photosensitizers based on the carbazole structure were designed and developed for cationic polymerization. Along with triarylsulfonium and diaryliodonium salts, the carbazole derivatives showed a high photosensitization effect in the cationic photopolymerization of epoxides. The photophysical properties of the carbazole derivatives were studied in terms of electronic absorption, fluorescence, and phosphorescence spectrometry. Moreover, a unique photosensitization mechanism of the carbazole derivatives was discussed after studies of the fluorescence quenching, redox behavior, and kinetics of the photopolymerization by time-resolved fluorescence spectrometry, cyclic voltammetry, and photo differential scanning calorimetry, respectively. The results confirmed the redox photosensitization of the carbazole derivatives in cationic polymerization. The photosensitization of the carbazole and its ring or N-alkylated derivatives occurred predominantly in singlet excited states at the rate of the diffusion limit, whereas the carbazole derivatives with carbonyl substituents sensitized onium salts via triplet excited states on the basis of the Rehm-Weller equation in the photoinduced electron-transfer process.

Photoinduced Electron Transfer Reactions for Macromolecular Syntheses

“…Phenothiazine and its derivatives are another class of efficient photosensitizers with excellent reducing properties. − In a similar manner, thioxanthones, − carbazoles, − curcumin, , quinoxaline and related structures, − and highly conjugated derivatives of thiophene ,− have been used as long wavelength photosensitizers. Moreover, several other studies have been reported on photosensitization of onium salts based on photoinduced electron transfer reactions for the initiation of cationic polymerization. ,− It was recently shown that ferrocenium salts can promote sensitization of onium salts via photoinduced electron transfer .…”

Synthesis of Micropillar Arrays via Photopolymerization: An in Situ Study of Light-Induced Formation, Growth Kinetics, and the Influence of Oxygen Inhibition

“…Indeed, camphorquinone/amine systems are another category of dual-component photoinitiator that provides chemical amplification and rapid polymerization , and can often be quite efficient. Yet, the oxidation of free radicals by onium salts, as in the case of CQ/OPPI, is an elegant and relatively flexible type of initiation for free radical as well as cationic polymerization and has thus garnered significant attention. ,,− Hence, we selected the CQ/OPPI system owing to its effectiveness in the photopolymerization of acrylate systems , successful use in self-trapping in our previous studies − as well as for the future opportunity to examine growth in cationic systems.…”

Cationic UV-Curing of Epoxidized Biobased Resins

“…Higher anionic dimension leads to lower nucleophilicity, and photogeneration of stronger acids. Therefore, even if the anions have no direct role in the photochemistry, their structural dimensions strongly influence the polymerization kinetics [ 32 , 33 ].…”