TY - JOUR
T1 - The singlet states of methyl cinnamate and methyl indenoate
AU - Lewis, Frederick D.
AU - Quillen, Suzanne L.
AU - Elbert, Jeffrey E.
AU - Schneider, Siegfried
AU - Geiselhart, Peter
N1 - Funding Information:
Electronic excitation of MC in the long-wavelength absorption band presumably populates the r,n*(a) state. Internal conversion to S, should be rapid in view of the small S, , S2, S, energy gaps. Simple enones such as acrolein have weakly fluorescent lowest n,T* singlet states [23] and thus the fluorescence of MC and MI might arise from S,. however, in view of the very short fluorescence lifetimes of MC and MI, it is possible that fluorescence originates from the originally populated n,ti*(a) state. This alternative is supported by the good agreement between the values of ki determined experimentally and from the integrated absorption spectrum. The absence of a solvent effect upon Tf or h,,, for the fluorescence of MI is also in better accord with a 7r,7r*v s. n,r* fluorescent state. The shorter lifetime of the fluorescent singlet state of MC vs. MI plausibly reflects the effect of torsion upon the energetics and configuration interaction of the lowest singlet states [13].
PY - 1989/5
Y1 - 1989/5
N2 - The fluorescence lifetimes of methyl cinnamate and methyl indenoate have been investigated by means of picosecond laser spectroscopy. Values of <3 ps and 15 ± 2 ps for these esters are significantly shorter than those previously reported for ethyl cinnamate. The short lifetimes are tentatively attributed to the competition between fluorescence from the originally populated π,π* singlet state and its internal conversion to a lowest n,π* singlet state. The efficiency of isomerization is independent of solvent, but dependent upon temperature and excitation wavelength. Comparison of the quantum yields for direct and triplet-sensitized dimerization indicates that intersystem crossing is highly inefficient. Thus the isomerization which occurs upon direct irradiation occurs predominantly from the singlet manifold.
AB - The fluorescence lifetimes of methyl cinnamate and methyl indenoate have been investigated by means of picosecond laser spectroscopy. Values of <3 ps and 15 ± 2 ps for these esters are significantly shorter than those previously reported for ethyl cinnamate. The short lifetimes are tentatively attributed to the competition between fluorescence from the originally populated π,π* singlet state and its internal conversion to a lowest n,π* singlet state. The efficiency of isomerization is independent of solvent, but dependent upon temperature and excitation wavelength. Comparison of the quantum yields for direct and triplet-sensitized dimerization indicates that intersystem crossing is highly inefficient. Thus the isomerization which occurs upon direct irradiation occurs predominantly from the singlet manifold.
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U2 - 10.1016/1010-6030(89)87063-7
DO - 10.1016/1010-6030(89)87063-7
M3 - Article
AN - SCOPUS:0011593415
SN - 1010-6030
VL - 47
SP - 173
EP - 179
JO - Journal of Photochemistry and Photobiology, A: Chemistry
JF - Journal of Photochemistry and Photobiology, A: Chemistry
IS - 2
ER -