Effect of substituents on the performance of N-carbazolyl double benzylidene ketones in visible/NIR light one/two-photon polymerization

Abstract

Developing high-performance photoinitiation systems with high sensitivity is of great significance in one/two-photon polymerization. Especially, photoinitiators with rapid photobleaching effects, deep curing abilities and potential for two-photon lithography have great commercial prospects. However, such photoinitiators often require complex organic synthesis, thus having relatively limited varieties. Double benzylidene ketone is widely used as a high-performance dye and can be constructed through a one-step classical aldol condensation reaction. The optimization of its structure often involves introducing extended conjugated structures or different terminal substituents. However, the synergistic impacts of side substituents with different electron effects are rarely studied. Here, six novel carbazolyl double benzylidene ketones with tert-butyl on the terminal position and F atom or N, N-dimethylamino groups substituted at the side position on conjugated structures are designed and prepared to explore the structure–activity relationships. Notably, results show that introducing electron-donating groups at both positions can effectively induce a redshift in the absorption spectra of molecules, and the introduction of an electron-withdrawing F atom on the side position induces impressive photobleaching during photopolymerization under visible LED irradiation. Moreover, CZs/MDEA with PETA exhibit fast writing speed and excellent nano-patterning capability under 780 nm laser in two-photon polymerization (TPP) and have potential applications in 3D microfabrication technologies.