Mechanism of Photoinduced Step Polymerization of Thiophene by Onium Salts: Reactions of Phenyliodinium and Diphenylsulfinium Radical Cations with Thiophene
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Abstract
Laser flash photolysis and EPR studies were performed to elucidate the mechanism of photoinduced step polymerization of thiophene by using diphenyliodonium (Ph2I+) and triphenylsulphonium (Ph3S+) ions as photoinitiators. Photoexcitation of these ions generated phenyliodinium (PhI•+) and diphenylsulphinium (Ph2S•+) radical cations, which were readily quenched by thiophene with rate constants of kq = 1.26 × 1010 and 1.7 × 105 M-1 s-1, respectively. The transient absorption spectra of the corresponding thiophene radical cations were not directly detectable because of the spectral overlap with the precursor salts. However, the related electron-transfer reaction was confirmed by quenching of the PhI•+ radical cation with bithiophene to form the radical cation of bithiophene, which absorb strongly at 420 nm. EPR studies also confirmed the proposed electron-transfer mechanism through the direct detection of the radical cation of thiophene.
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