Photophysical Transitions and Photochemical Reactions
Elementary Photophysical Transitions and
Photochemical Reactions
NSF REU June 09, 2023
1
From Photochemistry of Organic Compounds by Peter Kl
án and Jakob Wirz, 2009
Photochemistry’s
Icons
Why I am here.
2
3
Photo by Lilli Kasha ca. 1970
4
Intersystem Crossing
Demchenko, A. P.
et al.
Angew. Chem. Int. Ed.
2014,
53,
2-11.
5
Phosphorescence and the Triplet State
Gilbert N. Lewis , M. Kasha
J. Am. Chem. Soc.
1944
,
66
, 2100-2116
Naphthalene phosphorescence – triplet energies
6
External and Internal Heavy Atom Effects
α
-Chloron
aphthalene
is yellow in EtI, JCP, 1952
7
Singlet O
2
in Chemiluminescence and in Triplet
Energy Transfer
8
Double Proton Transfer in 7-Azaindole
Proton Transfer Spectroscopy
9
The Blue Daylily and Intramolecular
S
1
Proton Transfer in Flavonoids
10
The Kasha Guitar
Triplet Sensitization
11
12
Triplet Sensitized Stilbene Photoisomerization
Hammond, G. S.; Saltiel, J.
J. Am. Soc. Chem.
1962-1964.
The Saltiel Plot
The Photostationary State
1
t-St +
3
S*
3
t* +
1
S*
3
t*
3
p*
3
p*
1
t + (1-
)
1
c
1
c-St +
3
S*
3
c* +
1
S*
13
5 kcal/mol
62 kcal/mol
14
57 kcal/mol
Vertical Excitation
49 kcal/mol
Vertical Excitation
Nonvertical Triplet Energy Transfer
15
A
v
e
r
a
g
e
b
o
n
d
e
n
e
r
g
i
e
s
C
-
C
8
3
k
c
a
l
/
m
o
l
C
=
C
1
4
6
k
c
a
l
/
m
o
l
π
b
o
n
d
~
6
3
k
c
a
l
/
m
o
l
17
π
b
o
n
d
~
E
a
c
t
=
6
6
k
c
a
l
/
m
o
l
c
i
s
-
a
n
d
t
r
a
n
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2
-
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r
p
t
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o
n
.
18
Spin
States
T T T S
T T T S
19
Effect of Conjugation
Absorbance
20
Molecular Orbital Analysis of the Diels-Alder Reaction
The
diene
is the electron
donor
and the
dienophile
is the electron
acceptor
.
The concerted nature of the D-A reaction can be understood by
considering the interaction of the
HOMO of the diene
with the
LUMO of
the dienophile
(Fukui/Kyoto, Woodward/Harvard, Hoffmann/Harvard
now Cornell---Nobel prize in Chemistry)
1
9
6
5
1
9
8
1
21
22
HOMO Donor
LUMO Acceptor
Frontier Orbital Control of Diels-Alder Reaction
23
Electrocyclic reactions are stereospecific
24
R
o
t
a
t
i
o
n
i
n
t
h
e
s
a
m
e
d
i
r
e
c
t
i
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l
e
a
d
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t
o
a
b
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d
i
n
g
i
n
t
e
r
a
c
t
i
o
n
(
+
l
o
b
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+
l
o
b
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r
-
l
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b
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n
–
l
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b
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)
.
T
h
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S
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d
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c
t
i
o
n
s
.
25
R
o
t
a
t
i
o
n
i
n
o
p
p
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i
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a
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(
+
l
o
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+
l
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b
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o
r
-
l
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b
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n
–
l
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b
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)
.
T
h
e
r
e
a
c
t
i
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n
p
a
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s
e
s
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a
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T
S
i
n
b
o
t
h
d
i
r
e
c
t
i
o
n
s
.
26
27
Havinga, E.;
Schlatmann, J. L. M. A
Tetrahedron
1961,
16
, 146-152.
NEER, Havinga
NEER PRINCIPLE
27
Egbert Havinga
1909-1988
Havinga,
Tetrahedron
, 1973
ct
= 0.03,
tc
= 0.016
Havinga, E.; Schlatmann, J. L. M. A
Tetrahedron
1961,
16
, 146-152.
28
1,6-Dideuteriohexatrienes
28
ttt
-Ht
d2
in C
6
D
12
cct
-Ht
ctt
-Ht
Saltiel, J.; Redwood, C. E.; Laohhasurayotin, K.; Samudrala, R. Photochemistry
of the 1,6-Dideuterio-1,3,5-hexatrienes in Solution:
J. Phys. Chem. A
2018
,
122
, 8477-8489.
29
29
P
r
e
V
i
t
D
C
o
n
f
o
r
m
e
r
s
Havinga’s NEER Principle
Saltiel, J.: Cires, E.; Turek, A. (2004)
CRC Handbook of Organic
Photochemistry and Photobiology
,
2nd Edition (Scheme 1, p. 27-2)
Photocyclization
Long
Photoisomerization
Short
29
Egbert Havinga
1909-1988
NPE
conformers
NPE Conformers
30
31
Conformer specific photochemistry in
c
- and
t-
NPE
32
t
-NPE/Bz
33
Transposed
Matrix
Spectral Input
Matrix
Covariance
Matrix
Diagonalized
Matrix
Eigenvector Matrix
Eigenvectors
Eigenvalues
Number of
Components
Experimental
Spectra
S
i
=
i
V
+
i
V
i
=
V
S
i
,
i
=
V
S
i
S
i
=
i
V
+
i
V
Pure Component
Coefficients
A
,
A
and
B
,
B
Pure Component
Spectra
S
A
=
A
V
+
A
V
S
B
=
B
V
+
B
V
x
=
Summary of PCA-SM Mathematical Operations
34
35
t
-
N
P
E
/
P
C
A
-
S
M
330
350
370
390
410
430
450
470
490
510
, nm
-0.175
-0.115
-0.055
0.005
0.065
0.125
Normalized Intensity
Principal Eigenvectors
0
.
0
5
0
0
0
.
0
7
7
5
0
.
1
0
5
0
-
0
.
0
0
9
-
0
.
0
0
3
0
.
0
0
3
0
.
0
0
9
0
.
0
1
5
Plot
0
.
0
0
.
1
0
.
2
0
.
3
Standard Deviation
-0.0004
0.0013
0.0030
0.0046
0.0063
0.0080
[O
2
]/M
0.0
1.0
2.0
3.0
Global Stern-Volmer Plots
o
330
350
370
390
410
430
450
470
490
510
, nm
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Intensity
t
-NPE
B
t
-NPE
A
Conformer Spectra
t
-NPE
A
t
-NPE
B
36
S-V Kinetics
Stern-Volmer Quenching
37
The Stern-Volmer Plot
where I
a
is the rate of light absorption
38
39
Benzophenone State Diagram
40
El-Sayed’s Rules for Intersystem Crossing
41
42
43
44
45
Multidimensional Isomerization – Conical
Intersections –
Trapping Twisted Intermediates
B. G. Levine, T. J. Martínez.
Annu.
Rev. Phys. Chem.
2007
,
58
, 613-34.
Saltiel, J.; Gupta, S. Photochemistry of the Stilbenes in
Methanol. Trapping the Common Phantom Singlet State.
J.
Phys. Chem. A
2018
,
122
, 6089-6099.
46
47
48
48
A
c
k
n
o
w
l
e
d
g
m
e
n
t
s
Acknowledgments
PCA-SM
C. Redwood
L. Zimanyi
Experimental
Gosia Bayda,
Shipra Gupta
Sumesh Krishnan
Support
NSF (1965-2020)
49
50
The Saltiel Plot for Stilbene Triplet Photoisomerization
51
1,3-Diene Triplets: Conformer Specific
Photoisomerization and Photodimerization
Fluorenone sensitized photoisomerization
57 kcal/mol
52 kcal/mol
59 kcal/mol
Not present
52
1,3-Diene Triplets: Conformer Specific Photoisomerization
and Photodimerization
Fluorenone sensitized dimerization
53
Saltiel Plots
1,3-butadiene dimerization
dashes
1,3-pentadiene
E,Z
isomerization
solid line
54
55
Heptane - - -
Water
56
Delve into the fascinating world of photophysical transitions and photochemical reactions through a collection of images showcasing key concepts such as singlet oxygen, triplet states, proton transfers, and sensitization processes. Gain insights into the intricate mechanisms governing these phenomena in chemistry research.
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Elementary Photophysical Transitions and Photochemical Reactions NSF REU June 09, 2023 1
Photochemistrys Icons Why I am here. From Photochemistry of Organic Compounds by Peter Kl n and Jakob Wirz, 2009 2
Intersystem Crossing Demchenko, A. P. et al.Angew. Chem. Int. Ed. 2014, 53, 2-11. 4
Phosphorescence and the Triplet State Gilbert N. Lewis , M. Kasha J. Am. Chem. Soc. 1944, 66, 2100-2116 Naphthalene phosphorescence triplet energies 5
External and Internal Heavy Atom Effects -Chloronaphthalene is yellow in EtI, JCP, 1952 6
Singlet O2 in Chemiluminescence and in Triplet Energy Transfer 7
Double Proton Transfer in 7-Azaindole Proton Transfer Spectroscopy 8
The Blue Daylily and Intramolecular S1 Proton Transfer in Flavonoids 9
Triplet Sensitized Stilbene Photoisomerization The Saltiel Plot Hammond, G. S.; Saltiel, J. J. Am. Soc. Chem.1962-1964. 12
The Photostationary State 1 d[ t] dt d[ c] dt [ S*][ t] [ S*][ c] [ c] [ ] [ t] 1t-St + 3S* 3t* 3p* 3p* 1t + (1- )1c 1c-St + 3S* 3t* + 1S* = + = 3 1 1 [ S*][ t] [ p*] 0 k k t d 1 = + ) [ p*] 0 k = 3 1 1 [ S*][ c] (1 k c d 3c* + 1S* = = 3 1 1 [ p*] ) [ p*] ) k k t d 3 1 1 (1 k k c d 1 [ ] (1 [ ] k k t = PSS 1 c 13
62 kcal/mol 57 kcal/mol Vertical Excitation 49 kcal/mol Vertical Excitation 5 kcal/mol 14
H H CH3-CH3 C C Average bond energies C-C 83 kcal/mol C=C 146 kcal/mol bond ~ 63 kcal/mol H H H H H H
cis- and trans-2-butenes are stable separable isomers. They have the same connectivity and are stereoisomers. Rotation about a double bond occurs only at very high T or following light absorption. bond ~ Eact = 66 kcal/mol 18
SpinStates ( ( + + ) ) ( ( ) ) T T T S 19
Absorbance 170 nm 217 (21,000) 263 (52,500) 239 (3,400) 256 (8,000) max( ( max) ( )n n max x 10-3, M-1cm-1 28 53 80 86 max, nm Effect of Conjugation 1 2 3 4 294.1 328 348 404 20
Molecular Orbital Analysis of the Diels-Alder Reaction The diene is the electron donor and the dienophile is the electron acceptor. The concerted nature of the D-A reaction can be understood by considering the interaction of the HOMO of the diene with the LUMO of the dienophile (Fukui/Kyoto, Woodward/Harvard, Hoffmann/Harvard now Cornell---Nobel prize in Chemistry) 1965 1981 21
HOMO LUMO EWG 22
Frontier Orbital Control of Diels-Alder Reaction HOMO Donor LUMO Acceptor EWG 23
Electrocyclic reactions are stereospecific CH3 CH3 175 oC h CH3 CH3 CH3 h 175 oC CH3 24
Thermal reaction CH3 CH3 CH3 H3 C conrotatory Rotation in the same direction leads to a bonding interaction (+ lobe on + lobe or - lobe on lobe). The reaction passes through the same TS in both directions. 25
Photochemical reaction CH3 CH3 CH3 h H3 C disrotatory Rotation in opposite directions leads to a bonding interaction (+ lobe on + lobe or - lobe on lobe). The reaction passes through the same TS in both directions. 26
NEER PRINCIPLE * Havinga, Tetrahedron, 1973 ct = 0.03, tc = 0.016 hv * | florida state university | | florida state university | Egbert Havinga 1909-1988 * hv small_color_torches-new small_color_torches-new * hv * * Havinga, E.; Schlatmann, J. L. M. A Tetrahedron 1961, 16, 146-152. 27
1,6-Dideuteriohexatrienes ttt-Htd2 in C6D12 ctt-Ht cct-Ht C6D12 x tct 0.44 0.085 0.34 CD3CN x tct 0.54 0.093 0.39 0.014 ttt x ttt 0.245 x ctt cct tct ttt x 0.24 0.058 0.11 Saltiel, J.; Redwood, C. E.; Laohhasurayotin, K.; Samudrala, R. Photochemistry of the 1,6-Dideuterio-1,3,5-hexatrienes in Solution: J. Phys. Chem. A 2018, 122, 8477-8489. 28
Havingas NEER Principle PreVit PreVit D D Conform Conform ers ers R R Egbert Havinga 1909-1988 h H O H O H Pro Photocyclization Long (-)cZ(-)c R R h H O H O R H Lumi (+)cZ(+)c R OH Photoisomerization Short h H OH Tachy (+)tZ(-)c 29
NPE Conformers | florida state university | | florida state university | t-NPEA t-NPEB small_color_torches-new small_color_torches-new c-NPEA c-NPEB NPE conformers 30
Fluorescence Emission Spectra of t-NPE as a Function of exc in Ar Outgassed Benzene at 20 oC 1.0 t-NPE/Bz 0.8 | florida state university | | florida state university | Normalized Intensity exc = 320 nm exc = 345 nm exc = 350 nm 0.6 small_color_torches-new small_color_torches-new 0.4 0.2 0.0 330 350 370 390 410 430 450 470 490 510 33 , nm
Summary of PCA-SM Mathematical Operations Covariance Matrix Transposed Matrix Spectral Input Matrix x = Number of Components Eigenvalues Diagonalized Matrix Eigenvectors Eigenvector Matrix i = V Si, i =V Si Si = iV + iV Pure Component Spectra SA= AV + AV SB= BV + BV Experimental Spectra Si = iV + iV Pure Component Coefficients A, A and B, B 34
Plot Principal Eigenvectors Standard Deviation 0.125 0.0 0.1 0.2 0.3 0.015 Normalized Intensity 0.065 Stern-Volmer equation: 0.009 = 1 + KSV[Q] 0.005 0.003 -0.055 -0.115 -0.003 -0.175 330 350 370 390 410 430 450 470 490 510 , nm Global Stern-Volmer Plots -0.009 0.0500 Conformer Spectra 0.0775 0.1050 3.0 1.0 t t- -NPE/PCA NPE/PCA- -SM SM t-NPEA t-NPEB Normalized Intensity 0.8 t-NPEA 2.0 t-NPEB 0.6 o 0.4 1.0 Global Stern-Volmer equation: 0.2 A[Q] F0( )/F( )= 1 + KSV 0.0 -0.0004 0.0013 0.0030 0.0046 0.0063 0.0080 [O2]/M0.0 36 330 350 370 390 410 430 450 470 490 510 , nm
Stern-Volmer Quenching Equation Rate 1A + h exc 1A* Ia 1A* 1A + h f kf[1A*] kis[1A*] 1A* 3A* kp[1A*] 1A* P kq[Q][1A*] 1A* + Q 1A + Q* 37 S-V Kinetics
The Stern-Volmer Plot 1 d[ ] h k d[ ] h = = = o f f f k f= 1 k [ A*] f + + I dt k k k f dt 1 a f is p d[ A*] = + + 0 = 1 I ( )[ A*] k k k where Ia is the rate of light absorption a f is p dt I k = 1 [ A*] a k k + + k k = = f k f f is p f + + + + [Q] 1 k k k k [Q] f is p q q d[ ] I h k = f f a + + ( dt k k k f is p ) 1 = + [Q] 1 = + o f / [Q] k K f q SV 38
Multidimensional Isomerization Conical Intersections Trapping Twisted Intermediates ?? ? ? ?? ???? ?????= ?? ?? ????? B. G. Levine, T. J. Mart nez. Annu. Rev. Phys. Chem. 2007, 58, 613-34. Saltiel, J.; Gupta, S. Photochemistry of the Stilbenes in Methanol. Trapping the Common Phantom Singlet State. J. Phys. Chem. A2018, 122, 6089-6099. 46
Acknowledgments PCA-SM C. Redwood L. Zimanyi Experimental Gosia Bayda, Shipra Gupta Sumesh Krishnan Support NSF (1965-2020) 48
