噻吩硫化合物之光化學

Abstract

本研究是利用雷射光解瞬態吸收法，量測芳香基及非芳香基噻吩硫化合物之光解中間體之瞬態吸收光譜及反應動力學，並配合光化學產物分析來探討可能之反應機制。 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.