Bicarbazole‐based oxalates as photoinitiating systems for photopolymerization under UV–Vis LEDs

Abstract

Photoinitiators are critical to initiate chain reactions in photopolymerization. For such applications, the absorption of photoinitiator must be compatible with the emission of light sources and enables the fast manufacturing of threedimensional network or structures. Light-emitting diode (LED) is a new kind of energy-saving and environmental protection light source, exhibiting a substantial response in the near UV and visible range to replace the traditional mercury lamp and other light sources in photopolymerization. Here, we introduce methyl oxalate into bicarbazole chromophore (BiCz). By variation of the single or double substituents in the BiCz, we demonstrate that the absorption spectra can be adjusted and redshift to visible range and show good absorption in the near UV and visible range (365-475 nm). We explore their photochemistry based on experimental results and theoretical calculations and the mechanism of photoreactions have been verified. The super photostability by themselves and good hydrogen abstraction ability from amine co-initiator make them as excellent near UV and visible light active photoinitiators. Critically, the photoinitiation of the free-radical polymerization of acrylate monomers with low content (0.1% concentration) upon LED irradiation at 365-475 nm, exhibits excellent application potential in light curing and other fields. K E Y W O R D S photoinitiators, free-radical polymerization, UV-visible LEDs, high efficiency

Recent advances on carbazole-based oxime esters as photoinitiators of polymerization

“…[262] Choice of bicarbazole as the chromophore was supported by previous works of the same groups on another family of type I photoinitiators, namely bicarbazole-based oxalates. [263] Noticeably, by using a bicarbazole structure, a slight redshift of the absorption maxima was found for all oxime esters compared to the parent OXE-02 (See Figure 9 and Table 2). Even if only a minor variation of the absorption maxima was found between the different compounds, absorption spectra extending until 400 nm for BC-OXE-1-BC-OXE-3, 450 nm for BC-OXE-4 and BC-OXE-5 could be determined.…”

Fused carbazole–coumarin–ketone dyes: high performance and photobleachable photoinitiators in free radical photopolymerization for deep photocuring under visible LED light irradiation

“…A common method for red-shifting absorption is to modify structures through molecular engineering approaches, such as introducing chromophores and large conjugated structures, including carbazole, [25][26][27][28] stilbene, [29][30][31] pyrazoline, 32,33 and coumarin. [34][35][36][37] However, these visible LED PIs have limited applications.…”

Rationally designed Tröger's base decorated bis-carbazoles as twisted solid-state emitting materials and dead bacterial cell imaging

“…Similarly, bis-carbazoles, with two carbazole units linked through the 3-3 0 positions, with high Stokes shift belong to a class of molecules with numerous applications in organic electronics, sensors, and photovoltaics due to their low ionization potential, high thermal stabilities, as well as their blue luminescence. [24][25][26][27][28][29][30] Bis-carbazole scaffolds have also been utilized as potential host materials for phosphorescent OLEDs. The rationale behind this work relies on the exploration of the twisted architecture of Tro ¨ger's base as well as the intrinsic fluorescence properties of bis-carbazole scaffolds to design novel luminescent organic molecules.…”