TY - JOUR
T1 - Spectroscopic properties of spheroidene analogs having different extents of π-electron conjugation
AU - Frank, Harry A.
AU - Desamero, Ruel Z.B.
AU - Chynwat, Veeradej
AU - Gebhard, Ronald
AU - Van Der Hoef, Ineke
AU - Jansen, Frans Jos
AU - Lugtenburg, Johan
AU - Gosztola, David
AU - Wasielewski, Michael R
PY - 1997/1/9
Y1 - 1997/1/9
N2 - The spectroscopic properties of spheroidene and a series of spheroidene analogs with extents of π-electron conjugation ranging from 7 to 13 carbon-carbon double bonds were studied using steady-state absorption, fluorescence, fluorescence excitation, and time-resolved absorption spectroscopy. The spheroidene analogs studied here were 5′,6′-dihydro-7′,8′-didehydrospheroidene, 7′,8′-didehydrospheroidene, and 1′,2′-dihydro3′,4′,7′,8′- tetradehydrospheroidene and taken together with data from 3,4,7,8-tetrahydrospheroidene, 3,4,5,6-tetrahydrospheroidene, 3,4-dihydrospheroidene already published (DeCoster, B.; Christensen, R. L.; Gebhard, R.; Lugtenburg, J.; Farhoosh, R.; Frank, H. A. Biochim. Biophys. Acta 1992, 1102, 107) provide a systematic series of molecules for understanding the molecular features that control energy transfer to bacteriochlorophyll in photosynthetic bacterial light-harvesting complexes. All of the molecules were purified by high-pressure liquid chromatographic techniques prior to the spectroscopic experiments. The absorption spectra of the molecules were observed to red-shift with increasing extent of π-electron conjugation. The room temperature fluorescence data show a systematic crossover from dominant S1 → S0 (21Ag → 11Ag) emission to dominant S2 → S0 (11Bu → 11Ag) with increasing extent of conjugation. The S2 fluorescence quantum yields of all the carotenoids in the series were measured here and indicate that 3,4-dihydrospheroidene with nine carbon - carbon double bonds has an S2 quantum yield of (2.7 ± 0.3) × 10-4 which is the highest value in the series. The lifetimes of the S1 states of the molecules were determined from time-resolved transient absorption spectroscopy and found to decrease as the conjugated chain length increases. The transient data are discussed in terms of the energy gap law for radiationless transitions which allows a prediction of the S1 energies of the molecules. The implications of these results for the process of light harvesting by carotenoids in photosynthesis are discussed.
AB - The spectroscopic properties of spheroidene and a series of spheroidene analogs with extents of π-electron conjugation ranging from 7 to 13 carbon-carbon double bonds were studied using steady-state absorption, fluorescence, fluorescence excitation, and time-resolved absorption spectroscopy. The spheroidene analogs studied here were 5′,6′-dihydro-7′,8′-didehydrospheroidene, 7′,8′-didehydrospheroidene, and 1′,2′-dihydro3′,4′,7′,8′- tetradehydrospheroidene and taken together with data from 3,4,7,8-tetrahydrospheroidene, 3,4,5,6-tetrahydrospheroidene, 3,4-dihydrospheroidene already published (DeCoster, B.; Christensen, R. L.; Gebhard, R.; Lugtenburg, J.; Farhoosh, R.; Frank, H. A. Biochim. Biophys. Acta 1992, 1102, 107) provide a systematic series of molecules for understanding the molecular features that control energy transfer to bacteriochlorophyll in photosynthetic bacterial light-harvesting complexes. All of the molecules were purified by high-pressure liquid chromatographic techniques prior to the spectroscopic experiments. The absorption spectra of the molecules were observed to red-shift with increasing extent of π-electron conjugation. The room temperature fluorescence data show a systematic crossover from dominant S1 → S0 (21Ag → 11Ag) emission to dominant S2 → S0 (11Bu → 11Ag) with increasing extent of conjugation. The S2 fluorescence quantum yields of all the carotenoids in the series were measured here and indicate that 3,4-dihydrospheroidene with nine carbon - carbon double bonds has an S2 quantum yield of (2.7 ± 0.3) × 10-4 which is the highest value in the series. The lifetimes of the S1 states of the molecules were determined from time-resolved transient absorption spectroscopy and found to decrease as the conjugated chain length increases. The transient data are discussed in terms of the energy gap law for radiationless transitions which allows a prediction of the S1 energies of the molecules. The implications of these results for the process of light harvesting by carotenoids in photosynthesis are discussed.
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U2 - 10.1021/jp962373l
DO - 10.1021/jp962373l
M3 - Article
AN - SCOPUS:0031560540
SN - 1089-5639
VL - 101
SP - 149
EP - 157
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 2
ER -