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Studies on meta effect appears in dioxetane chemiluminescence and ester photolysis

二氧杂环丁烷化学发光和酯光解中出现meta效应的研究

基本信息

批准号：
11440212
负责人：
FUJIMORI Ken
金额：
$ 7.42万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

Photolysis of m- and p-methoxybenzyl acetates (I_m and I_p) in methanol has been investigated and found the followings : (a) Photochemical C-O bond fission of I_m occurs from the excited singlet state, while that of I_p occurs from the triplet state ; (b) Φ_r apparently lower for I_m photolysis than for I_p is due to internal return of intimate pairs, I.e., the C-O bond fission quantum yield is 1 for I_m while 0.8 for I_p. c C-O bond cleavage of the excited singlet state of I_m occurs so readily that photolysis produce a singlet radical pair and ion pair origin products accompanied by extremely low fluorescence. Because C-O bonding splits slowly in the excited singlet state of I_p, intersystem crossing becomes the major pathway for excited singlet state reactions, resulting in a moderate yield of fluorescence and a high yield of the triplet state, and eventually yielding free radical origin products. The major factor determining I photolysis products is the relative rate of C-O bond cleavage in the excited singlet state versus intersystem crossing. The reason why C-O bond cleavage of excited singlet state of I_m is very fast while that of I_p is slow has been studied by quantum mechanical theory.When 3-methoxy-3-(w- and p-methoxyphenyl)-4,4-adamantiliden-l ,2-dioxetane (II_m, II_p) is photolyzed in a glassy matrix at 77K, adamantanone adjacent to S_l state of methyl methoxybenzoate plays as an external machine to alter electron spin multiplicity of the ester from S_l to T_l, by the energy return, mechanism, p-orbital overlapping between the ester and adamantanone is necessary to work the energy return mechanism between methyl m-methoxybenzoate and adamantanone. Intimate pair ofmethyl p-ethoxybenzoate and adamantanone generated through photolysis of II_p in glassy matrix at 77K forms exciplex. Energy transfer business that occurs immediately after the II_p fragmentation between two carbonyl fragments determines fate of ehemiluminescenee.

研究了间、对甲氧基乙酸苄酯(I_m和I_p)在甲醇中的光解，发现：(A)I_m的光化学C-O键断裂发生在激发单重态，而I_p的光化学C-O键断裂发生在三重态；(B)I_m光解的Φ_r明显低于I_p，这是由于紧密键对的内返，即I_m的C-O键分裂量子产额为1，而I_p的C-O键分裂量子产额为0.8。由于激发态Ip的C-O键在激发态下裂解较慢，体系间交叉成为激发态反应的主要途径，从而产生适中的荧光产额和较高的三重态产额，最终产生自由基源产物。决定I光解产物的主要因素是激发态单重态C-O键断裂相对于系间交叉的相对速率。用量子力学方法研究了激发态I_m单重态C-O键断裂很快而I_p激发态C-O键断裂较慢的原因。当3-甲氧基-3-(w-和对-甲氧基苯基)-4，4-金刚烷-L在77K光解时，2-二氧杂环己烷(II_m，II_p)在玻璃基质中光解时，与S_L态相邻的金刚烷酮作为外机，通过能量返回、机制将酯的电子自旋多重数从S_L改变为T_L。酯和金刚烷酮之间的P轨道重叠是间甲氧基苯甲酸甲酯和金刚烷酮之间能量返回机制所必需的。对乙氧基苯甲酸甲酯与金刚烷酮在77K时在玻璃基质中光解生成亲密对，形成激基络合物。在两个羰基片段之间的Ii_p裂解后立即发生的能量转移决定了Ehemiluescen的命运。