標題: Direct Observation of the Solvent Effects on the Low-Lying ne and pi pi* Excited Triplet States of Acetophenone Derivatives in Thermal Equilibrium
作者: Narra, Sudhakar
Shigeto, Shinsuke
應用化學系
應用化學系分子科學碩博班
Department of Applied Chemistry
Institute of Molecular science
公開日期: 5-三月-2015
摘要: Low-lying excited triplet states of aromatic carbonyl compounds exhibit diverse photophysical and photochemical properties of fundamental importance. Despite tremendous effort in studying those triplet states, the effects of substituents and solvents on the energetics of the triplet manifold and on photoreactivity remain to be fully understood. We have recently studied the ordering of the low-lying n pi* and pi pi* excited triplet states and its substituent dependence in acetophenone derivatives using nanosecond time-resolved near-IR (NIR) spectroscopy. Here we address the other important issue, the solvent effects, by directly observing the electronic bands in the NIR that originate from the lowest n pi* and pi pi* states of acetophenone derivatives in four solvents of different polarity (n-heptane, benzene, acetonitrile, and methanol). The two transient NIR bands decay synchronously in all the solvents, indicating that the lowest n pi* and pi pi* states are in thermal equilibrium irrespective of the solvent polarity studied here. We found that the pi pi* band increases in intensity relative to the n pi* band as solvent polarity increases. These results are compared with the photoreduction rate constant for the acetophenone derivatives in the solvents to which 2-propanol was added as a hydrogen-atom donor. Based on the present findings, we present a comprehensive, solvent- and substituent-dependent energy level diagram of the low-lying n pi* and pi pi* excited triplet states.
URI: http://dx.doi.org/10.1021/jp512494m
http://hdl.handle.net/11536/124517
ISSN: 1520-6106
DOI: 10.1021/jp512494m
期刊: JOURNAL OF PHYSICAL CHEMISTRY B
Volume: 119
起始頁: 3808
結束頁: 3814
顯示於類別:期刊論文