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

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 pi 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-pi-D-pi-D molecules, the A-pi-D-pi-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. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2692-2700