抄録
Methylene blue borate(MB.Ph3RB) is a stable salt in the dark and readily proceeds electron transfer (ET) to produce a neutral radical pair upon irradiation by visible light. The unstable boranyl radical undergoes the carbon-boron cleavege to generate active alkyl radical immediatly, along with MB dye bleaching. The association state of salt plays an important role in controlling the photophysical and photochemical properties. The photoinduced ET rate of MB borate in the tight ion pair state (ket 9×10-11 s-1) which predominatly exists in non-polar solution, is far greater than that observed in the free solvated ion state in polar solvents. Photopolymerization of MMA in CH3CN solution not occurs with MB borate(MB Ph3RB) alon, but undergoes with MB Ph3RB/Et4NPh3RB combination system. Addition of weak H-donor, such as methanol, results in a great rate-acceleration. The photoinitiation mechanism and different influences were also discussed.
Photoinduced electron-transfer reactions play a central role in many proc of technological importance, such as silver halide sensitization, electrophotography and photoinduced polymerization[1]. However, the quantum yields of such reactions, in general, are very low, which means that the most part of incident photon energy is wasted[2.3]. This is mainly due to rapid exothermic back electron transfer to reform the starting materials, which occurs within the formed radical ion pair in competition with chemical reaction [2.3]. Recently the electron transfer reaction followed by rapidly bond cleavage, in which one or both two of ion radical in the pair is unstable with respect to fragmentation into an ion and a free radical, has attracted a great interesting to design new high efficient photosensitized initiation system for visible photopolymerization[4.5]. In the previous papers[6, 7], we have proposed a type of electron transfer sensitization system composed different xanthene dyes as electron donor and aryliodonium salts as electron acceptor in the form of ion pair. The latter rapidly undergoes G-I bond cleavege through electron transfer from excited dye to iodonium salt to afford a radical species capable of initiation. In this paper we report other type of electron transfer photosensitization system for polymerization, in which triphenylalkyl borate employed as electron donating activator in combination with cationic dyes as excited electron acceptor, ouch ae thiazene. Their spectral propertiee, photochemical behaviors and application for polymerization were studied kinetically.
