Dynamics of charge recombination processes in the singlet electron-transfer state of pyrene-pyromellitic dianhydride systems in various solvents. Picosecond laser photolysis studies
Dynamics of charge recombination processes in the singlet electron-transfer state of pyrene-pyromellitic dianhydride systems in various solvents. Picosecond laser photolysis studies
复制标题
各种溶剂中芘-均苯四甲酸二酐体系单线态电子转移态电荷复合过程的动力学。
DOI：
10.1021/j100286a016
复制
发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Y. Kanda
中科院分区：
文献类型：
--
作者：
N. Mataga;H. Shioyama;Y. Kanda
为了阐明即使在乙腈溶液中，在可见光区具有CT吸收带的强电子供体和受体的配合物被光激发也不会产生游离离子自由基的潜在机制，用皮秒激光光谱法对不同溶剂中芘-焦二酸酐（PMDA）体系进行了详细的时间分辨瞬态吸收光谱测量和时间分辨荧光测量。在苯溶液中，光激发形成了寿命400-ps的弱荧光电子转移（ET）态，而在极性更强的溶剂中，由于电荷重组（CR）失活，形成了寿命短得多的非荧光双离子对。在所有被检测的溶液中，从双离子对解离成自由离子不能与CR失活竞争，CR失活在极性更强的溶剂中由于离子对和中性基态之间的能隙减小而变得更快。结果表明，在乙腈中激发的芘与未激发的PMDA相遇产生的离子对比激发基态配合物产生的离子对结构更松散，CR速率常数更小。
In order to elucidate the underlying mechanisms showing that no dissociated ion radicals are produced even in acetonitrile solution when some complexes of the strong electron donors and acceptors with CT absorption bands in the visible region are photoexcited, the authors have made detailed time-resolved transient absorption spectral measurements and time-resolved fluorescence measurements upon the pyrene-pyromellitic dianhydride (PMDA) system in various solvents with picosecond laser spectroscopy. A weakly fluorescent electron-transfer (ET) state with 400-ps lifetime is formed by photoexcitation in benzene solution, while nonfluorescent geminate ion pairs with much shorter lifetimes due to the charge recombination (CR) deactivation are formed in more polar solvents. In all solutions examined, dissociation into free ions from the geminate pair cannot compete with the CR deactivation which becomes faster in more polar solvents due to the decrease of the energy gap between the ion pair and neutral ground state. Moreover, it has been demonstrated that ion pairs produced by encounter between excited pyrene and unexcited PMDA in acetonitrile have more loose structure and show a smaller CR rate constant than those produced by exciting the ground-state complex.