chm 5175: part 2.2 introduction to molecular photophysics 1 ken hanson mwf 9:00 – 9:50 am office...
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CHM 5175: Part 2.2
Introduction to Molecular Photophysics
Ken HansonMWF 9:00 – 9:50 am
Office Hours MWF 10:00-11:00
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RainbowsGlassesMirage
Refractometer
Moon LightButterfly Wings
Sea ShellsSoap Bubbles
Two-slit expHolograms
Shadow Blur
Sand in WaterSunsets
UV-VisFluorometry
TASolar Cells
Interaction of Light with Matter
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Narrowing Our Focus• Absorption/Transmission• Visible spectrum
Visible Light (hn)
Electronic Transitions- electrons excited from one energy level to another.
• Atomic• Molecular• MaterialsSample
Interaction of Light with Matter
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e-p+
Hydrogen Absorption
Higher ELower E
hn
e-
p+
Ground State Excited State
hn
Energy
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2 2
1 1H
l h
E Rn n
Hydrogen Absorption
“white” light source Hydrogen Sample Prism
Line Spectrum
H
Rydberg Formula
HH
H
H
H
H
1 e-
80 e-
10 e-
Increasing Complexity
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N
N
N
N
N
PtCl250 e-
Atomic Transitions (movement of electrons)
+ Molecular Transitions
(movement of electron density)
Transitions
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N
N
N
N
N
PtCl
e-p+
hn
e-
p+
Atomic Transitions
hn
N
N
N
N
N
PtCl
Molecular Transitions
hn
hn
C O
R
R
C H
R
R
R
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Types of Molecular Transitions
σ - σ*max < 150 nm
p - p*max 200 - 800 nm
C C
R
R R
R
n - p*max 150 - 300 nm
C
O
H
HH
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C H
R
R
R
Types of Molecular Transitions
High energy photons
• methane = 125 nm
• ethane = 135 nm
Ground State Excited State
hn
Bonding
Antibonding
σ - σ*max < 150 nm
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Types of Molecular Transitions
p - p*max 200 - 800 nm
Visible photons
• benzene = 260 nm
• tetracene = 500 nm
hn
Bonding
Antibonding
C C
R
R R
R
Ground State Excited State
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C O
R
R
n
n
Types of Molecular Transitions
n - p*max 150 - 300 nm
Visible photons
• acetone = 280 nm
• pyridine = 270 nm
hn
Non-Bonding
Antibonding
Ground State Excited State
C OR
R
C OR
R
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Types of Molecular Transitions
σ - σ*max < 150 nm
p - p*max 200 - 800 nm
n - p*max 150 - 300 nm
C
O
H
HH
400300200 500100
p - p*
n - p*s - s*
Wavelength (nm)
Abso
rptio
n
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Types of Molecular Transitions
Metal Centered (MC)max 200 –800 nm
[Co(H2O)6]2+
MMCTmax 300 –800 nm
NN
NN
N
NRuII
MLCTmax 300 –1000 nm
LMCTmax 300 –1000 nm
MnO4-
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Types of Molecular Transitions
[CoCl4]2-
[Co(H2O)6]2+
Metal Centered (MC)
d-d transitionsmax 200 – 800 nm
M M + L
t2g
eg
• 3d and 4d transition metals (+ ligands)
• Relatively weak (0-1000 M−1cm−1)
• Early structural determination
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Types of Molecular Transitions
• Low-lying empty ligand orbital
• Low oxidation state metal (electron rich)
• High d orbital energy
NN
NN
N
NRuII hn
e-
Metal-to-Ligand Charge Transfer (MLCT)max 300 – 1000 nm
250 300 350 400 450 500 550 6000
2
4
6
8
10
(10
4 M
-1cm
-1)
Wavelength (nm)
MLCT
p - p* M M + L
t2g
eg
L
p*
NN
NN
N
NRuIII (-)
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Types of Molecular Transitions
• Ligand with high E lone pairs (S or Se)
• Metal with low-lying empty orbitals
Ligand-to-Metal Charge Transfer (LMCT)max 300 – 1000 nm
M M + L
t2g
eg
L
p
Mn-O4-
O2- (p) Mn7+
Purple
e-
Cd-SS2- (p) Cd2+
Yellow
e-
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Types of Molecular TransitionsMetal-to-Metal Charge Transfer (MMCT)
max 300 – 800 nm
MMCTe-
M1
M1 + L
M2
M2 + L
II
III
t2g
eg
t2g
eg
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C N Mn
O
O
L
L
Fe
N
N
L
L
Types of Molecular Transitions
t2g
eg
eg
t2g
p
p*
M1
M1 + M2 + L
M2
600500400 700300
MCLMCT
MLCT
Wavelength (nm)
Abso
rptio
n
MMCT
e- e-
e-
Vo
V4
V3
V2V1
Complete Diagram
σ - p*p - p*
n - p*
MC
LMCT
MLCT
MMCT
σ - σ*
n - σ*
Transitions
Vo
V4
V3
V2V1
Vo
V4
V3
V2V1
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Energy
E0
E1
E2
Transitions
Electronic
Vibrational
Rotational
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Vo
V4
V3
V2V1
Vo
V4
V3
V2V1
Vo
V4
V3
V2V1
Complete Diagram
Energy
E0
E1
E2
S0
S1
S2
Jablonski Diagram
Transitions
Electronic
Vibrational
Rotational
Energy
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Complete Diagram
ExcitationInternal Conversion
Fluorescence
S0
S1
S2
Jablonski Diagram
Non-radiative decay
Energy
Ground State (S0)
First Excited State (S1)
Second Excited State (S2)
22Singlet Triplet
Spin Flip
Complete Diagram
S0
S1
S2
Jablonski Diagram
Energy
hn
Ground StateS0
Singlet Excited StateS1
ExcitationInternal Conversion
FluorescenceNon-radiative decay
Nicholas J. Turro, Principles of Molecular Photochemistry
Triplet/Singlet Excited States
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Triplet
Singlet
Lower Energy
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Ground State
Singlet Excited State
hspin-orbit coupling
Triplet Excited State
Ground State
h
Spin-Orbit Coupling
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Quantum Numbersn = Principal
l = Angular
ml = Magnetic
ms = Electron spin
Heavy Atoms Pt, Ir, I...
Nicholas J. Turro, Principles of Molecular Photochemistry
Spin-Orbit Coupling
Rotating Chair and Bicycle Wheel
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Jablonski Diagram
ExcitationInternal Conversion
FluorescenceNon-radiative decayIntersystem Crossing
PhosphorescenceS0
S1
S2
Energy T1
T2
27Nicholas J. Turro, Principles of Molecular Photochemistry
Jablonski Diagram of Anthracene
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• Electron transfer• TICT• ESIPT• Photochemical
ReactionsExcitationInternal Conversion
FluorescenceNon-radiative decayIntersystem Crossing
Phosphorescence
Other Processes
S0
S1
S2
Energy T1
T2
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Excited State Electron Transfer
NN
NN
N
NRuII
hn
NN
NN
N
NRuIII (-)
e-e-
+ A RuIII(bpy)3 + A-
+hn
e-
+
RuII(bpy)3 [RuII(bpy)3]* A RuIII(bpy)3 A-
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Photosynthesis
Excited State Electron Transfer
31Nicewicz, D. A.; MacMillan, D. W. C. Science 2008, 322, 77-80.
Photocatalytic α-alkylation of aldehydes
Excited State Electron Transfer
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Excited State Structural Change
+ h
*
Twist + CT*
+ h
Twisted Intramolecular Charge Transfer
N
CN
e-
e-
Pratt et al. J. Chem. Phys. 2005, 122, 084309
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ESIPT
reverse proton transfer
absorption emission
OH
N
OH
N O
N
H
O
N
H
Excited State Structural ChangeExcited State Proton Transfer
NH
N
N
N
N
OH
OH
NH
N
HN
N
N
OH
O
Hanson et al. Org. Lett. 2011, 13, 1598
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Photochemical ReactionsPhotopolymerization
Peachy Printer ($100)
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Photochemical ReactionsPhotolithography
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Photochemical ReactionsPhotoisomerization
hn
Ground State Excited State
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Photochemical ReactionsPhotoswitches
J. Am. Chem. Soc., 2013, 135 (16), pp 5974–5977
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ProcessesExcitation
FluorescencePhosphorescence
Non-radiative decayInternal conversion
Intersystem crossingPhotochemistry
S0
S1
S2
E T1
T2
“Complete” Jablonski Diagram
Product
Product
Measurement Technique
Absorption Spectroscopy
Fluorescence Spectroscopy
Transient Absorption Spectroscopy
Solar Cell Testing
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Side Note: Other ExcitationsThermal Excitation
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Side Note: Other ExcitationsChemical Excitation
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Side Note: Other ExcitationsSonoluminescence
Side Note: Other Excitations
Nature 2008, 455, 1089–1092.
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Tribo/Fractoluminescence
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Side Note: Other ExcitationsElectroluminescence
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OH
N
N
NO2
Para Red
NN
NH2
H2N
Fast Brown
NNO3S
HO
SO3
Sunset Yellow (Food Yellow 3)
Side Note: Dye Structure
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Bright Blue Common Food Uses Beverages, dairy products, powders, jellies, confections, condiments, icing.
Royal Blue Common Food Uses Baked goods, cereals, snack foods, ice-cream, confections, cherries.
Orange-red Common Food Uses Gelatins, puddings, dairy products, confections, beverages, condiments.
Lemon-yellow Common Food Uses Custards, beverages, ice-cream, confections, preserves, cereals.
Orange Common Food Uses Cereals, baked goods, snack foods, ice-cream, beverages, dessert powders, confections
Side Note: Dye Structure
Molecular Photophysics End
Any Questions?