from Light Absorption to Solar Fuels - Carnegie Mellon …AtifiilPht th iArtificial Photosynthesis...
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A tifi i l Ph t th i fArtificial Photosynthesis – from Light Absorption to Solar Fuels
Devens GustDepartment of Chemistry and BiochemistryArizona State UniversityTempe AZ 85287 1604 USATempe, AZ 85287-1604 USA
ASU Center for Bioenergy and Photosynthesis
ASU Center for Bio-Inspired Solar Fuel Production
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Best current “technology” for solar energy conversion photosynthesis
The source of most of our current energy
energy conversion- photosynthesis
current energy – fossil fuels1014 kg of carbon removed from thefrom the atmosphere each year and converted to fuelfuel1021 Joules of energy each year
CO2 + H2O (CH2O) + O2light
~125 TW(10 times humanneeds)2 2 ( 2 ) 2 needs)
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Artificial photosynthesis
Exploiting the physics and chemistry underlying photosynthesis for y g p ytechnological purposes
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How does photosynthesis work?
A AAntenna
Antenna
© Sinauer Associates, Inc.
Dark chemical reactions
Catalysts for H2O oxidation, CO2reduction and biofuel production (carbohydrate
Antennas
Light capture, excitation energy migration regulation
Reaction centers
Charge separation, electrochemical energy
4
production, (carbohydrate, biodiesel, hydrogen)
migration, regulation
and photoprotection
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How does photosynthesis work?
A AAntenna
Antenna
© Sinauer Associates, Inc.
5
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Reaction centersReaction centers
Q
htt // f h h tN W db D t t f Ch i t d Bi h i t
Bacterial reaction center
QB
6
http://www.fuchs-research.netN. Woodbury, Department of Chemistry and Biochemistry, Arizona State University
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Artificial reaction centers
•+ •-
+ -Molecular photovoltaicsMolecular photovoltaics
SKuciauskas, D.; Liddell, P. A.; Lin, S.; Stone, S. G.; Moore, A. L.; Moore, T. A.; Gust, D. J. Phys. Chem. B 2000, 104, 4307
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Light absorptionhν
C-P-C60
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Light absorption
C 1P CPorphyrin first excited singlet state
C-1P-C60
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Photoinduced electron transfer
e-
3 picoseconds3 picoseconds
(3 x 10-12 s)
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Photoinduced electron transfer
•+
•-
C P•+ C • Charge separated stateC-P•+-C60•− Charge-separated state
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Charge recombination
•+
•-
C P•+ C • 3 nanosecondsC-P•+-C60•−
e-3 nanoseconds(3x10-9 s)
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Charge shift reaction
•+e-
•-
e
C P•+ C • 67 picosecondsC-P•+-C60•− 67 picoseconds
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Light energy stored asLight energy stored as electrochemical energy
•+ •-
C •+ P C • Final charge separated stateC •+ -P-C60•− Final charge-separated state
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Light energy stored asLight energy stored as electrochemical energy
C •+ -P-C60•−
Yield of charge separated state ~ 100%
Stored energy ~1.0 electron volt
Lifetime = hundreds of ns at room temp.
•+ •-
Lifetime hundreds of ns at room temp.
1 microsecond at 8K
Dipole moment ~160 DSmirnov, S. N.; Liddell, P. A.; Vlassiouk, I. V.; Teslja, A.; Kuciauskas, D.; Braun, C. L.; Moore, A. L.; Moore, T. A.; Gust, D. J. Phys. Chem. A, 2003, 107, 7567
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Artificial antenna systemsLH2 Photosynthetic antenna
Rhodopseudomonas acidophilaRhodopseudomonas acidophila
R. Cogdell,
N. Isaacs
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A funnel-like antenna – RC complex
Terazono, Y.; Kodis, G.; Liddell, P. A.; Garg, V.; Moore, T. A.; Moore, A. L.; Gust, D. J. Phys. Chem. B 2009, 113, 7147-7155
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Energy and electron transferEnergy and electron transfer
Time constants for photochemical processes (ps)
process free base 7 hexad 2 heptad 1porphyrin hexad porphyrin fullerenezinc
process free base 7 hexad 2 heptad 1 2-meTHF 2-meTHF 1,2-DFB 1,2-DFB
step 1 0.4 0.4 0.4d 0.4
step 2 5 - 14 5 - 14 5 - 13 5 - 13
step 3 8 7 7d 7 step 4 4 6 6 6 step 5 5 - 26 4 - 21 2 - 15 2 - 15
pstep 6 570 230 230 step 7 4800 1500 1500 step 8 3 step 9 230
Both energy transfer to the porphyrins and photoinduced electron transfer are highly efficient.
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Regulation and photoprotectionRegulation and photoprotection
Sunlight is diffuse, so photosynthesis uses antennas to maximize delivery of excitation energy to reaction centers.energy to reaction centers.If the sunlight intensity suddenly increases, photosynthesis is overdriven. Singlet oxygen, reactive radicals redox intermediates andreactive radicals, redox intermediates, and other destructive species are produced.Photosynthetic organisms have evolved y gregulatory mechanisms to down-regulate delivery of excitation energy to reaction centers under such conditions. (e.g., “non-ce e s u de suc co d o s (e g , ophotochemical quenching, NPQ”)
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Regulation in nanotechnologyRegulation in nanotechnologyFunctional nanoscale systems, yincluding artificial photosynthesis, will need self-regulation and control circuits.gHow can we design photocatalysts or other molecular components that areother molecular components that are not only functional, but also adaptive, responding to changes in theirresponding to changes in their environment?
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Self-regulation of photoinduced electron transfer by a molecular nonlinear transducer
Antenna
Charge separation unit
C
Antenna
Control unit
Straight, S. D.; Kodis, G.; Terazono, Y.; Hambourger, M.; Moore, T. A.; Moore, A. L.; Gust, D. Nature Nanotechnology 2008, 3, 280
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Photochromic control unitPhotochromic control unit
HNBlue light
HNDHI BTHN
NO
CNNC
g
Heat, Red light
HN
NO CN
NC
DHIdihydroindolizine
BTbetaine
0.5
0.6
0.2
0.3
0.4
Abs
orba
nce
at 6
85 n
m0 50 100 150 200
0.0
0.1
White Light Intensity (mW)
A a
White light intensity
Photostationary distribution
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Principle of operationPrinciple of operationOMehν
OMePETτcs = 2.2 ns
NNH N
HNN
ON
CH3
H
Φcs = 82%
τcr = 14 ns
HN
NO
H
MeO
MeO
CNNC
hνDHI
Photochrome in colorless form
hνcolorless form –electron transfer
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Principle of operationOMe
Principle of operationhν
OMe
hνNo PET
NNH N
HNN
ON
CH3
H
Φcs ~1%
HN
NO CN
H
MeO
MeO
NC
hν Singlet energy
BTPhotochrome in energy transfer quenching
τent = 33 psPhotochrome in colored form – no electron transfer
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Principle of operationPrinciple of operation
Isomer ratio, and therefore the amount of Blue light Heat, red light
(low QY) quenching, is determined by white light intensity and temperature
(low QY)
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Operationp
Quantum yield of chargeQuantum yield of charge separation is reduced from 82% at low light to as low as 27% under bright white light.27% under bright white light.
The overall yield of charge separation is a non-linear function of white light intensityfunction of white light intensity
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Comparison with natural NPQComparison with natural NPQ
synt
hetic
on
tran
spor
tP
hoto
sel
ectro
Photon flux density
Self regulation in Natural regulation inSelf-regulation in molecular system
Natural regulation in orange trees
Ribeiro, R. V.; Machado, E. C. Braz. J. Plant Physiol. 2007, 19, 393-411.
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Photocatalytic water splittingPhotocatalytic water splitting
W. J. Youngblood, S.-H. A. Lee, Y. Kobayashi, E. A. Hernandez-Pagan, P. G.Hoertz, T. A. Moore, A. L. Moore, D. Gust, T. E. Mallouk, J. Am. Chem. Soc., 2009,131, 926-927
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ConclusionsConclusionsPhotosynthetic principles can guide the design of artificial systems that convertdesign of artificial systems that convert sunlight into useful forms of energy– Antenna function– Photoinduced charge separation– Regulation and photoprotection– Production of useful fuels or electricityy
Such systems are in general not yet practical for technological applications morefor technological applications – more research is needed
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Many thanks to
Tom Moore, Ana Moore, Tom Mallouk, Sergei Smirnov, Chuck Braung ,Many students and postdocs – listed on the slidesthe slidesThe Department of Energy and National Science Foundation for fundingScience Foundation for funding