Solvent Effects on the S0(11Ag-) S2(11B
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- 作者：Zhenguo Chen ; Changyoul Lee ; Thomas Lenzer ; Kawon Oum
- 刊名：Journal of Physical Chemistry A
- 出版年：2006
- 出版时间：October 5, 2006
- 年：2006
- 卷：110
- 期：39
- 页码：11291 - 11297
- 全文大小：160K
- 年卷期：v.110,no.39(October 5, 2006)
- ISSN：1520-5215
文摘
Solvent-induced spectral shifts of the four C40 carotenoids, 
mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-carotene, echinenone, canthaxantin, andastaxanthin, have been studied in supercritical CO2 and CF3H. In situ absorption spectroscopic analysis wasused to determine the maximum peak position of the electronic transitions from the ground state (11Ag-) tothe S2 state (11Bu+) of the carotenoids. The medium polarizability function, R(n) = (n2 - 1)/(n2 + 2) of therefractive index of the solvent was varied over the range R(n) = 0.08-0.14, by changing the pressure of CO2or CF3H between 90 and 300 bar at the temperature 308 K. For all the carotenoids studied here, a significanthypsochromic shift of ca. 20-30 nm was observed in supercritical fluids as compared to that in nonpolarliquids. The spectral shifts in supercritical fluids were compared with those in liquids and showed a clearlinear dependence on the medium polarizability. The temperature-dependent shift of the absorption maximawas less significant. Interestingly, there was almost no difference in the energetic position of the absorptionmaxima in supercritical CO2 and CF3H at a given R(n) value. This is in contrast to previous extrapolationsfrom studies in liquids at larger R(n) values, which yielded different slopes of the R(n)-dependent spectralshifts for polar and nonpolar solvents toward the gas-phase limit of R(n) = 0. The current experimentalresults in the gas-to-liquid range show that the polarity of the solvent has only a minor influence on the11Ag- mages/entities/rarr.gif"> 11Bu+ transition energy in the region of low R(n). We also obtain more reliable extrapolations ofthis 0-0 transition energy to the gas-phase limit mages/gifchars/nu.gif" BORDER=0 >0-0gas-phase mages/entities/ap.gif"> (23 000 ± 120) cm-1 for mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-carotene.