S sub 1 and T sub 1 species of. beta. -carotene generated by direct photoexcitation from the all-trans, 9-cis, 13-cis, and 15-cis isomers as revealed by picosecond transient absorption and transient Raman spectroscopies

Journal Article · Thu Apr 18 00:00:00 EDT 1991 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100161a022· OSTI ID:5543814

Hashimoto, Hideki; Koyama, Yasushi ^[1]; Hirata, Yoshinori; Mataga, Noboru ^[2]

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1. Kwansei Gakuin Univ., Nishinomiya (Japan)
2. Osaka Univ., Toyonaka (Japan)

Time-resolved absorption spectra, upon excitation of the all-trans, 9-cis, 13-cis, and 15-cis isomers of {beta}-carotene, were recorded by using 20-25-ps, 355-nm pump and white-continuum interrogating pulses. The isomers showed the S{sub n} {l arrow} S{sub 1} absorption at 556 (all-trans), 565 (9-cis), 560 (13-cis), and 562 (15-cis) nm; no time-dependent changes of the absorptions were detected. (The S{sub 1} lifetimes for the all-trans and 15-cis isomers were determined precisely, by using 0.5-ps pump and interrogating pulses, to be 12.4 {plus minus} 0.5 and 14.0 {plus minus} 0.5 ps, respectively.) After the decay of the S{sub n} {l arrow} S{sub 1} absorption, a weak absorption ascribable to the T{sub n} {l arrow} T{sub 1} transition remained in the 510-520-nm region, from which the quantum yield of intersystem crossing was estimated to be on the order of 10{sup {minus}3}. Transient Raman spectra were recorded by using 355-nm pump and 532-nm probe mode-locked (76 MHz), Q-switched (800 Hz) pulse trains (pulse duration {approximately} 100 ps). An S{sub 1} Raman spectrum was extracted by subtraction between a pair of pump-and-probe spectra with different delay times, i.e. 0 and 500 ps. A T{sub 1} Raman spectrum was extracted by subtracting a probe-only spectrum from a pump-and-probe spectrum with the delay time 500 ps. Each isomer showed a unique S{sub 1} Raman spectrum, which was interpreted by assuming the configuration of the particular isomer. On the other hand, the 13-cis and 15-cis isomers showed T{sub 1} Raman spectra that are essentially the same as that shown by the all-trans isomer, the 9-cis isomer showed a unique T{sub 1} Raman spectrum. The above results indicate (1) that no isomerization takes place in the S{sub 1} state and (2) that the T{sub 1} state is generated through intersystem crossing.

• OSTI ID: 5543814
• Journal Information: Journal of Physical Chemistry; (United States), Vol. 95:8; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
14 SOLAR ENERGY
CAROTENOIDS
RAMAN SPECTRA
VISIBLE SPECTRA
ABSORPTION SPECTROSCOPY
ENERGY LEVELS
EXCITED STATES
EXPERIMENTAL DATA
ISOMERS
LASER SPECTROSCOPY
MOLECULAR STRUCTURE
RAMAN SPECTROSCOPY
SAMPLE PREPARATION
TIME RESOLUTION
TRANSIENTS
DATA
HYDROCARBONS
INFORMATION
NUMERICAL DATA
ORGANIC COMPOUNDS
PIGMENTS
RESOLUTION
SPECTRA
SPECTROSCOPY
TERPENES
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