Conjugated Carbazole‐Based Schiff Bases as Photoinitiators: From Facile Synthesis to Efficient Two‐Photon Polymerization

Abstract

Exploration of simple and economical synthetic routes to construct active two-photon initiators (2PIs) with long conjugation length is highly desirable to promote the development of two-photon-induced photopolymerization technology. In this article, several conjugated carbazole-based derivatives containing N=C bonds as π bridges and electron donor/acceptor groups were prepared through one-step Schiff base reaction. The structure-activity relationship was systematically investigated through calculations and experimental tests. The results showed that compared to the D-π-D-π-D molecules, the A-π-D-π-A molecules exhibited stronger charge transfer, which induce redshifted linear absorption and enhanced two-photon absorption at 800 nm. The 2PIs displayed aggregation-induced emission property and show potential for the fabrication of luminescent microdevices. In two-photon-induced microfabrication tests, the formulations containing novel 2PIs exhibited lower threshold energy than the widely used commercial photoinitiator Irgacure 369 and the two-photon resists IP-L is the brand name of the two-photon resist from Nanoscribe, specially designed for nanoscribe's laser lithography systems.

Cleavable Unimolecular Photoinitiators Based on Oxime‐Ester Chemistry for Two‐Photon Three‐Dimensional Printing

“…Currently two‐photon 3D printing has been mainly limited to academic research due to its low printing speed . To promote two‐photon 3D printing into the market, development of efficient two‐photon initiators (2PIs), a key compound in photoactive formulations, is highly desirable to guarantee fast printing rates, a reduced polymerization threshold, and finally fabricated structures with a high resolution . An efficient 2PI should have large two‐photon absorption (2PA) to ensure efficient photon absorption, and an efficient initiation mechanism, through which the absorbed energy can be efficiently used to generate active initiation species .…”

Conjugated Ketocarbazoles as Efficient Photoinitiators: From Facile Synthesis to Efficient Two-photon Polymerization

“…The σ 2PA of the photoinitiators were measured by z-scan technique, and the experimental setup has been described earlier [27]. Rhodamine B was used as reference to verify the reliability of the experimental setup.…”

Conjugated Bifunctional Carbazole‐Based Oxime Esters: Efficient and Versatile Photoinitiators for 3D Printing under One‐ and Two‐Photon Excitation

“…In this paper, four bifunctional photocleavable PIs comprising oxime‐ester moieties and conjugated carbazoles were designed and synthesized. We have shown that the conjugated carbazoles are good visible light chromophores and have excellent two‐photon sensitivity . Therefore, introduction of oxime‐ester moieties as latent initiation functionalities into the conjugated carbazole skeleton should provide efficient PIs sensitive to visible and near‐infrared light.…”

“…We have shown that the conjugated carbazoles are good visible light chromophores and have excellent two-photon sensitivity. [29] Therefore, introduction of oxime-ester moieties as latent initiation functionalities into the conjugated carbazole skeleton should provide efficient PIs sensitive to visible and near-infrared light. The effect of different substitution positions (4 a and 4 c) on the structureproperty relationship and the impact of different types of radials (4 c and 4 d) on the photoinitiating behavior ( Figure 1) were systematically studied.…”