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Yu, X. Jia, D. Han, T. Zhou, J. Yang, J. Nie and T. Wang, Polym. Chem., 2015, DOI: 10.1039/C5PY00502G.
Polymer Chemistry RSC
This journal is © The Royal Society of Chemistry 2013 J. Name., 2013, 00, 1-3 | 1
Aromatic amine-sulfone/sulfoxide conjugated D–π–
A–π–D type dyes in photopolymerization under 405nm and 455nm laser beams
Mengqiang Wang,a,b Xiaoyu Ma, b Jinghua Yu,b Xiaoqin Jia, b Dandan Han, b Tengfei
Zhou, b Jinliang Yang ,b Jun Nieb and Tao Wang*a,b
Based on a D–π–A–π–D structural strategy, six novel dyes (Cz-SO, Cz-SO2, TA-SO, TASO2, PTZ-SO, and PTZ-SO2) containing triphenylamine/phenothiazine/carbazole as electron donors and sulfone/sulfoide as electron acceptors are prepared and incorporated into a photoinitiating system, together with iodonium salt (ONI). The one- and two-photon photophysical properties of these dyes were studied. The UV-vis spectra showed red-shifts of 51 and 75 nm from N-ethyl carbazole (CZ) to Cz-SO and Cz-SO2. Similar red-shifts were found in the other dyes. The two-photon excited fluorescence (TPEF) spectra in the range 700-880 nm were measured and it was found that these dyes present a clear two-photon absorption (TPA). Among them, PTZ-SO2 possesses the maximum TPA cross-section which is 2465.5 GM. Ring-opening cationic polymerization of epoxides and free radical polymerization of acrylates upon exposure to very soft irradiation of laser diodes at 405 nm and 455 nm were performed using ONI/dyes initiating systems. Compared with the wellknown camphorquinone-based systems, the combinations of the obtained dyes with iodonium salt exhibit higher polymerization efficiency. The results from photo bleaching and electrochemical experiments show that these dyes could photosensitize ONI through photoinduced charge transfers. Owing to their higher polymerization efficiency and large
TPA cross-section, these dyes would have extensive application prospects in the flields of photopolymerization by soft visible light irradiation sources and two-photon polymerization (TPP). 1 Introduction
Photoinitiated polymerization is a well-known technique used in many technologically important areas.1-3 The recent development of cheap and easily accessible light-emitting diodes (LEDs) operating on soft visible light irradiations has opened new fields for photoinitiated polymerization. Compared with UV irradiation sources, soft visible light irradiation sources are more convenient and avoid UV rays. For polymer synthesis at soft irradiation conditions, the design and development of excellent photoiniators in the visible light wavelength range is a very challenging task.4 However, exploring new photoinitiators used for radical photopolymerization, especially for cationic photopolymerization at soft irradiation conditions, is difficult.
Dye photosensitized photopolymerization reactions have been largely known for many years and typically encountered in various photopolymerizations. The design and synthesis of new chemical skeletons used as photosensitizers are easier than those of new photoinitiators. Recently, real progress has been made in the synthesis of new chemical skeletons and in the use of new additives, which has allowed the proposal of a large number of novel photoinitiating systems.5-8 Several commercial dyes can be used in visible light induced photopolymerization, such as camphorquinone and anthraquinone derivatives.
Chemically modified conventional UV sensitive photoinitiators were also found to be efficient visible light photosensitizers, such as chemically modified benzophenone derivatives,9-11 chemically modified thioxanthone derivatives,12 and chemically modified 2,2’-dimethoxy-2-phenylacetophenone derivatives. 13
Newly developed dyes applicable in visible light sensitive photoinitiating systems include purple or blue light sensitive dyes, green light sensitive dyes, red light sensitive dyes, and so on.5.,6,14
In cationic photopolymerization systems, onium salts,
Page 1 of 12 Polymer Chemistry
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ARTICLE Journal Name 2 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 2012 especially diaryliodonium salts, are widely used as photoinitiators because of their simple synthesis, absence of color, and high photoinitiating efficiency. However, the absorption of these salts generally occurs below 350 nm, which limits their applications under visible light. Several electronrich polynuclear aromatic compounds, such as anthracene, pyrene, and perylene, have been reported to increase the spectral sensitivities of diaryliodonium salts in visible light and are especially attractive and efficient photosensitizers. Crivello and coworkers reported several carbazole and phenothiazine compounds bearing cationically polymerizable vinyl, vinyl ether, and epoxide groups.15-20 These monomers are rapidly and efficiently polymerized or copolymerized by UV irradiation in the presence of onium salt photoinitiators.Several mechanisms explain the photosensitization of onium salts; however, the most efficient and generally applicable process for this class of photoinitiators is electron-transfer photosensitization. In these photosensitizing systems, diaryliodonium salt shows good electron-accepting ability with dyes.