Photochemistry of Thienosultines
Dr . Niann S. Wang
我們以 248 nm 波長之雷射光光解 5-methyl-7-phenylthienosultine
(7) 及 4-methyl-6-phenylthienosulfolene (8)，二者所得到的中間體之最大吸收峰均在 370 nm ，此中間體易被其基態分子焠熄，其自我焠熄速率常數 ksq (108 M-1 s-1) 值分別為 9.46 及 2.62 ，此速率常數不受溫度之變化影響。在焠熄劑之動力學實驗中，顯示二者都易與三重態之氧分子反應，其焠熄反應速率常數值 kq (109 M-1 s-1) 分別為 3.62 及 3.17 ，而與單重態之焠熄劑 (如Acrylonitrile) 反應之 kq (106 M-1 s-1) 則僅在，顯示前述二者之中間體皆為三重態。
藉由光化學產物分析，得知 Sultine 7 經 254 nm 之照光會形成Sulfolene 8 ，若加入焠熄劑 FN (Fumaronitrile) 於溶劑中，則產生環化加成產物，再加上 ESR 光譜分析之結果，推論 Sultine 7 經光解後會由三重態激態上的碳氧鍵斷裂形成三重態的反應中間體。|
A laser flash photolysis-transient absorption system was employed to study the spectroscopies and kinetics of intermediates produced by photodissociation of aryl and non-aryl thienosultines. Possible mechanisms are proposed after combining our results and the results of a steady-state photolysis study. Absorption band peaks at 370 nm was recorded for both intermediates, which were produced by photodissociation of 5-methyl-7-phenylthienosulti -ne (7) and 4-methyl-6-phenylthienosulfolene (8) with an excimer laser output at 248 nm. The intermediates were quenched effectively by their parent molecules. The self-quenching rate constants were determined to be 9.46 and 2.62 × 108 M-1 s-1 , respectively , and were independent of temperature. In addition, we found both intermediates were quenched effectively by O2 , a triplet state quencher, with a rate constant of 3.62 and 3.17 × 109 M-1 s-1 , respectivetly , but were less effectively quenched by singlet quenchers, such as acrylonitrile, with a rate constant of about 106 M-1 s-1. We concluded that the observed intermediates were in their triplet states. Combining the results of a study of steady-state photochemistry and ESR experiment, we proposed the reaction mechanism , for the photochemistry processes.