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Photopolymerization of 7,7′-coumarinyl polymethylene dicarboxylates: Fluorescence and kinetic study

✍ Scribed by Yun Chen; Rong-Tzung Hong

Publisher
John Wiley and Sons
Year
1997
Tongue
English
Weight
235 KB
Volume
35
Category
Article
ISSN
0887-624X

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✦ Synopsis

All eight 7,7 -(4-methylcoumarinyl) polymethylene dicarboxylates ( 3, 4) containing terminal photoreactive coumarin chromophores show strong fluorescence intensities at room temperature in dimethyl sulfoxide (DMSO) and CH 2 Cl 2 . After irradiation with 350 nm light for 2 h, the fluorescence characteristics of the dicarboxylates reveal their photopolymerization paths. On irradiation of the unsubstituted dicarboxylates (3) in DMSO, singlet excited state excimers are formed, leading to syn head-tohead coumarin dimer configuration. However, for all dicarboxylates in CH 2 Cl 2 , the dimerization of the coumarin chromophore proceeds via a triplet excited state in the presence of benzophenone to form the anti-configuration photoproducts. Further confirmations of the reaction mechanism are made by kinetic studies. At high concentration, photopolymerization of 7,7 -(4-methylcoumarinyl) polymethylene dicarboxylate (4c) obeys zero-order and first-order kinetics for coumarin chromophore and benzophenone, respectively. This is a powerful proof of the proposed mechanism of a triplet excited state reaction.

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