Introduction to Photochemistry and Light Upconversion · Introduction to Photochemistry and ......
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Introduction to Photochemistry and Light Upconversion Tomoyasu Mani Department of Chemistry University of Connecticut 10/29/2019 1 CT Japan Photochemistry Workshop
Transcript of Introduction to Photochemistry and Light Upconversion · Introduction to Photochemistry and ......
Introduction to Photochemistry and Light Upconversion
Tomoyasu ManiDepartment of ChemistryUniversity of Connecticut
10/29/2019 1
CT Japan
Photochemistry Workshop
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Department of Chemistry at the University of Connecticut
• @ Storrs, CT• 26 tenure‐track or tenured professors• Located in the Chemistry Building • 65 cutting‐edge research and teaching labs
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From Low to HighUpconversion Based on Triplet-Triplet
Annihilation
https://mani.chem.uconn.edu/photochem-workshop/
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© Science Media Group.
Energy Flows High to Low
©The McGraw‐Hill
Potential Energy
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Energy Flows Low to High ??
©The McGraw‐Hill
Potential Energy
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What is Photochemistry?
The chemistry concerned with the chemical effects of light. Generally, a chemical reaction is caused by using UV, visible, infrared light.
700 nm 400 nm600 nm 500 nm
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Why Important?
Photosynthesis is Driven by Light! We can see “inside” by Light!
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Converting Light to Something Else.
Making Molecules with Light. Making Electricity from Light.
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What is Going On? General Jablonski Diagram
FluorescencePhotonAbsorption
Ener
gyS3
S2
S1
IC
Ground State
Singlet Manifold
IC = internal conversion
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Photoexcitation = Excess Energy
FluorescencePhotonAbsorption
Ener
gyS3
S2
S1
IC
Ground State
Singlet Manifold
IC = internal conversion
Excited
GroundState
11https://cen.acs.org/biological-chemistry/biotechnology/Chemistry-Pictures-Laser-activated/97/web/2019/08
Fluorescence Emission
BLUE Light
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What is Going On? General Jablonski Diagram
FluorescencePhotonAbsorption
Ener
gyS3
S2
S1
IC
Ground State
Singlet Manifold
Triplet-tripletabsorption
T3
T2
T1
Phosphorescence*
ISC 2J
Triplet Manifold
ISC = intersystem crossing*in some molecules, quantum yield of phosphorescence can be as high as 0.3-0.5 at room temperature.
IC = internal conversion
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Photoexcitation = Excess Energy
FluorescencePhotonAbsorption
Ener
gyS3
S2
S1
IC
Ground State
Singlet Manifold
IC = internal conversion
Excited
GroundState
TripletExcited
isc
phosh
T1
S1
S0
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Spins: Singlet vs Triplet State
MS=0
Singlet S=0
isc
phosh
T1
S1
S0
MS=0 MS=-1MS=1
MS=0
Singlet S=0
Triplet S=1
(spin-forbidden transition, hence T1 state is long-lived)
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Images from1Universal Display Corporation2Schultz, D. M.; Yoon, T. P., Science, 343, 1239176 (2014)3Sakadžić, S. et al.; Nature Methods, 7, 755 (2010)4Castano, A. P. et al., Nat. Rev. Cancer, 6, 535 (2006)
Triplet Excited States in ActionPhotodynamic Therapy in Medicine
Photoredox Catalysts
Light Emitting Diodes
New TechnologiesSinglet fission etc…
Oxygen Sensing in vivo
Phosphorescence lifetime3
Singlet Oxygen Generation4
PHOLED1
Organic Synthesis2
A Peculiar Case of Molecular Oxygen (O2)
The ground electronic state is Triplet! Labeled as 3O2.
This is GOOD for us.
But, this may NOT be good for triplet excited states of other molecules
as they can readily react with molecular oxygens.
T1 + 3O2 → GS + 1O2
So, if you want to use triplet excited states, you need to work around the
problem of molecular oxygen,17
18https://cen.acs.org/biological-chemistry/biotechnology/Chemistry-Pictures-Laser-activated/97/web/2019/08
Energy Flows From High to Low
BLUE Light
Photon Upconversion: Convert Low-Energy Photon to High-Energy Photon
The sequential absorption of TWO or more photons leads to the emission of light (ONE photon) at shorter wavelength than the excitation wavelength.
700 nm 400 nm600 nm 500 nm
Higher EnergyLower Energy
Normal
Upconversion19
What is Triplet-Triplet Annihilation (TTA)?
T1+T1 [T1T1] S1 + S0
• Two triplet excited states form one singlet excited state (S1) and one singlet ground state (S0).
• It leads to delayed fluorescence from S1• TTA is opposite to singlet fission.
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Sensitized Triplet-Triplet Annihilation
SS1
SS0
ST1AT1
AS1
AS0
kISCkFTTET
kFTTA
kBTTET
kBTTA
1Parker, C.A.; Hatchard, C. G.; Proc. Chem. Soc. London 1962, 147.Picture is taken from Sing-Rachford, T. N.; Castellano, F. N.; Coord. Chem. Rev. 2010, 254, 2560.
Convenient way to produce TTA. Visible absorption by sensitizers with excellent extinction
coefficients. One of the upconversion mechanisms.
Donor‐Sensitizer Acceptor‐Annihilator
Delayed fluorescence
hVisible excitation
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Energy Transfer(TTET)
TTA Experiment: Green to Blue Upconversion
SS1
SS0
ST1AT1
AS1
AS0
kISCkFTTET
kFTTA
kBTTET
kBTTA
Donor‐Sensitizer Acceptor‐Annihilator
Delayed fluorescence
hVisible excitation
GREEN
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BLUE
DPA
PdOEP
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Blue Filter
Optical SetupHow do we see Blue Light?
Filter
Green LaserPointer
Sample
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What are you going to do with Molecular Oxygen?
1. Conventional Method
Deoxygenate solutions = Remove Oxygen
2. What We Do
Use Gels*!
“Embed” sensitizers and annihilators in gel matrix = Block Oxygen Diffusion
25*Duan, P.; Yanai, N.; Nagatomi, H.; Kimizuka, N. J. Am. Chem. Soc. 2015, 137, 1887–1894.
