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Journal of the Korean Chemical Society (JKCS)

ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 39, Number 4
JKCSEZ 39(4)
August 20, 1995 

Time Resolved ESR Studies on Short-Lived Reaction Intermediates Produced by Laser Photolysis of Anthraquinone in Organic Solvents
Daeil Hong*, Young-Hyoun Yun, Moo-Jeong Sohn, Kyung-Chan Kim, Keiji Kuwata
Anthraquinone이 유기용매에서 광반응에 의하여 반응 중간체로 생성하는 짧은 수명의 중성 세미퀴논 라디칼과 음이온 라디칼을 시간분해 ESR법에 의하여 측정하였다. 2-propanol(PrOH)과 triethylamine(TEA) 10:1 혼합 용매에서 광반응에 의하여 생성하는 중성 anthrasemiquinone 라디칼(AQH·)과 음이온 라디칼 (AQ·-)의 CIDEP 스펙트럼을 측정하였다. 생성한 AQH·은 반감기가 0.8μsec로 수명이 아주 짧았으며, AQ·-은 안정하여 cwESR의 측정이 가능하였다. 스핀분극된 음이온 라디칼(AQH·-*)의 분극소멸 속도 상수는 2.6×105 sec-1이고, 음이온 라디칼의 소멸은 1차 반응으로 속도상수가 3.0×102 sec-1이다. 혼합용매에 TEA가 2% 미만일 때 CIDEP가 일어나지 않았다. 벤젠과 TEA 혼합용매에서는 반감기 3.0 μsec의 중성 anthrasemiquinone 라디칼의 CIDEP 가 측정되었다. 그러나, cwESR은 측정되지 않았다. PrOH, TEA, 또는 벤젠만의 용매로서는 CIDEP와 ESR을 측정할 수 없었다.

The measurments of neutral semiquinone radicals, which were formed from the laser flash photolysis of anthraquinone (AQ) in the mixed solvents were carried out by the time resolved electron spin resonance (trESR) spectroscopy. The chemically induced dynamic electron polarization (CIDEP) spectra of the neutral semiquinone radical (AQH·) and semiquinone radical anion (AQ·-) were successively detected in the laser flash photolysis of AQ in the mixtures of 2-propanol (PrOH) and triethylamine (TEA). The neutral semiquinone radical was short-lived with the half-life of 0.8 μsec, whereas the semiquinone radical anion was relatively stable and then its cwESR could be observed. The rate constant of the spin-depolarization of semiquinone radical anion was 2.6×105 sec-1 and the decay of the radical anion was the first order reaction with the rate constant of 3.0×102 sec-1. No CIDEP of semiquinone radical anion was observed in the mixture of PrOH and the lower concentration of TEA than 2 percent. The CIDEP spectrum of the neutral semiquinone radical was detected in the mixture of benzene and TEA with the half-life of 3.0 μsec. The neutral semiquinone radical could not be detected by cwESR. Neither CIDEP nor ESR absorption could be observed in PrOH, TEA or benzene only.

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