A laser flash photolysis study of thiophenesultines
Li Yang, Luo
|Abstract:||本研究利用雷射光解法量測□吩硫化物的瞬態吸收光譜及其與淬滅劑之反應動力學，並分析其光化學產物以探討可能之應機制。以266 nm的雷射光解雙苯基□吩sultine和sulfolene，得到兩者光解後中間體的最大吸收均在340 nm。與氧氣的二級反應速率大約為接近擴散極限速率。
由溫度效應實驗中發現sultine 33光解後中間體衰變之活化能量為21.3 kJ / mol，而sulfolene 34光解後中間體之活化能為12.1 kJ / mol。經由光化學產物分析得知sultine 33經254 nm光解後會與淬滅劑產生環化加成產物，但sulfolene 34則否。而且由ESR分析得知兩者經254 nm光解後之中間體均有三重態之訊號，所以推論其反應機制可能為sultine 33與sulfolene 34光解後之中間體均為三重態，且sultine的中間體會經過碳硫鍵的斷裂，但sulfolene的中間體則不經此過程。
A laser Photolysis system has been used to study the absorption spectra and kinetics with quenchers of the transient intermediates of thiophenesultines. The intermediates, produced by photolyzing 5,7-diphenylthiophenesultine and 4,6-diphenylthiophenesulfolene with Nd:YAG laser output at 266 nm, both absorb strongly at 340 nm. From the temperature effect studies of the decay of intermediates, we obtained the activation energy 21.3 kJ / mol for sultine, and 12.1 kJ / mol for sulfolene. Both intermediates decay biexpontentially. We obtained the quenching rate of about 109 M-1 s-1 by oxygen, 106 M-1 s-1 by fumaronitrile , and 107 M-1 s-1 by N-phenylmalemide, The photochemistry of both compounds were also studied. Cycloadducts were obtained when 5,7-diphenylthiophenesultine, but not 4,6-diphenylthiophenesulfolene, was irradiated by 254 nm in the presence of trapping agents. The ESR spectra of thiophenesultine and thiophenesulfolene were recorded after being irradiated with 254 nm light. The spectra showed the characters of triplet species, implying the triplet state of intermediates for thiophenesultine and thiophenesulfolene photolysis at 266 nm. The intermediate of thiophenesultine photoolysis would proceed further the carbon-sulfur bond breaking, but not the intermediate of thiophenesulfolene. We also observed that the intermediate of thiophenesultine procceed self-quenching reaction at a constant of about 108 M-1 s-1. Polarization induced by the two phenyl groups may be attributed to this phenomenon.
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