TY - JOUR
T1 - Carotenoids as electron or excited-state energy donors in artificial photosynthesis
T2 - An ultrafast investigation of a carotenoporphyrin and a carotenofullerene dyad
AU - Pillai, Smitha
AU - Ravensbergen, Janneke
AU - Antoniuk-Pablant, Antaeres
AU - Sherman, Benjamin D.
AU - Van Grondelle, Rienk
AU - Frese, Raoul N.
AU - Moore, Thomas
AU - Gust, Devens
AU - Moore, Ana
AU - Kennis, John T M
PY - 2013/4/7
Y1 - 2013/4/7
N2 - Photophysical investigations of molecular donor-acceptor systems have helped elucidate many details of natural photosynthesis and revealed design principles for artificial photosynthetic systems. To obtain insights into the factors that govern the partition between excited-state energy transfer (EET) and electron transfer (ET) processes among carotenoids and tetrapyrroles and fullerenes, we have designed artificial photosynthetic dyads that are thermodynamically poised to favor ET over EET processes. The dyads were studied using transient absorption spectroscopy with ∼100 femtosecond time resolution. For dyad 1, a carotenoporphyrin, excitation to the carotenoid S 2 state induces ultrafast ET, competing with internal conversion (IC) to the carotenoid S1 state. In addition, the carotenoid S 1 state gives rise to ET. In contrast with biological photosynthesis and many artificial photosynthetic systems, no EET at all was detected for this dyad upon carotenoid S2 excitation. Recombination of the charge separated state takes place in hundreds of picoseconds and yields a triplet state, which is interpreted as a triplet delocalized between the porphyrin and carotenoid moieties. In dyad 2, a carotenofullerene, excitation of the carotenoid in the S2 band results in internal conversion to the S1 state, ET and probably EET to fullerene on ultrafast timescales. From the carotenoid S1 state EET to fullerene occurs. Subsequently, the excited-state fullerene gives rise to ET from the carotenoid to the fullerene. Again, the charge separated state recombines in hundreds of picoseconds. The results illustrate that for a given rate of EET, the ratio of ET to EET can be controlled by adjusting the driving force for electron transfer.
AB - Photophysical investigations of molecular donor-acceptor systems have helped elucidate many details of natural photosynthesis and revealed design principles for artificial photosynthetic systems. To obtain insights into the factors that govern the partition between excited-state energy transfer (EET) and electron transfer (ET) processes among carotenoids and tetrapyrroles and fullerenes, we have designed artificial photosynthetic dyads that are thermodynamically poised to favor ET over EET processes. The dyads were studied using transient absorption spectroscopy with ∼100 femtosecond time resolution. For dyad 1, a carotenoporphyrin, excitation to the carotenoid S 2 state induces ultrafast ET, competing with internal conversion (IC) to the carotenoid S1 state. In addition, the carotenoid S 1 state gives rise to ET. In contrast with biological photosynthesis and many artificial photosynthetic systems, no EET at all was detected for this dyad upon carotenoid S2 excitation. Recombination of the charge separated state takes place in hundreds of picoseconds and yields a triplet state, which is interpreted as a triplet delocalized between the porphyrin and carotenoid moieties. In dyad 2, a carotenofullerene, excitation of the carotenoid in the S2 band results in internal conversion to the S1 state, ET and probably EET to fullerene on ultrafast timescales. From the carotenoid S1 state EET to fullerene occurs. Subsequently, the excited-state fullerene gives rise to ET from the carotenoid to the fullerene. Again, the charge separated state recombines in hundreds of picoseconds. The results illustrate that for a given rate of EET, the ratio of ET to EET can be controlled by adjusting the driving force for electron transfer.
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U2 - 10.1039/c3cp50364j
DO - 10.1039/c3cp50364j
M3 - Article
C2 - 23435870
AN - SCOPUS:84874829349
SN - 1463-9076
VL - 15
SP - 4775
EP - 4784
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
IS - 13
ER -