Bicarbazole-based oxime esters as novel efficient photoinitiators for photopolymerization under UV-Vis LEDs

Abstract

Five novel oxime ester type photoinitiators based on the bicarbazole structure were designed and synthesized to extend the absorption wavelength range of photoinitiators to the near-ultraviolet–visible (UV–vis) region and ensure the high efficiency of photoinduced polymerization. Introducing alkyl chains with different lengths and/or cyclizations and further α-carbonyl groups influenced absorption and photolysis properties. The rationality of the designed molecules was proven by using UV–vis spectra, and liquid chromatography–mass spectrometry (LCMS) and in situ 1H NMR experiments were also performed to explain the mechanism of photoinduced degradation. Importantly, the photopolymerization and storage stabilities of the optimized photoinitiators in photocuring formulations were also tested and were found to be better than those of commercial photoinitiators, e.g., OXE 02.