TWO-PROTON PHOTOTAUTOMERIZATION DYNAMICS OF 7-AZAINDOLE COMPLEXES -Tapas Chakraborty Indian...
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Two-proton Phototautomerization Dynamics of 7-Azaindole Complexes
-Tapas Chakraborty
Indian Association for the Cultivation of Science Calcutta, India
TK02, OSU ICMS 2013
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Tautomeric forms of 7-azaindole Tautomeric forms of 7-azaindole
N N
H
N N
H
S0
S1
4.2
eV
2.8
eV
Normal Tautomer
0.65 eV (~ 15 kcal/mol )
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Double proton transfer phenomenon Double proton transfer phenomenon
UV light
300 nm
Taylor, El-Bayoumi and Kasha, PNAS, 63 (1969) 253
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Taylor, El-Bayoumi and Kasha, PNAS, 63 (1969) 253UV light
< 300 nm
DPT 1.1 ps
260 280 300 320
Wavelength (nm)
N N
H
N N
NN
HH
~470 nm
Tautomer emission
Fluorescence spectra
Wavelength (nm)300 350 400 450 500 550
~320
nm
>350
nm
Normal emission
Absorption spectra10-5 M
10-3 M
Double proton transfer phenomenon Double proton transfer phenomenon
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UV light
< 300 nm
DPT 1.1 ps
Key Issues
•Double Proton Transfer sequence :Concerted vs Stepwise
•Role of exciton interactions
•Medium effect
•Double Proton Transfer Barrier (1.5 kcal/mol)
Double proton transfer phenomenon Double proton transfer phenomenon
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UV light
< 300 nm
DPT 1.1 ps
Key Issues
•Double Proton Transfer sequence :Concerted vs Stepwise
•Role of exciton interactions
•Medium effect
•Double Proton Transfer Barrier (1.5 kcal/mol)
Double proton transfer phenomenon Double proton transfer phenomenon
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Double proton transfer barrier (original expt.) Double proton transfer barrier (original expt.)
Estimated barrier: 1.4 kcal/mol
F2
F1
N N
H
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Tautomerization under jet-cooling condition (Tautomerization under jet-cooling condition (10 K) 10 K)
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(7-azaindole)(7-azaindole)22 is synthesized in Ar matrix is synthesized in Ar matrix
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Inert gas (Ne, Ar, N2, etc.) crystals pack in Face-Centered cubic lattice structures
Pimentel (1922-1989)
(7-azaindole)(7-azaindole)22 is synthesized in Ar matrix is synthesized in Ar matrix
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3600 3400 3200 3000 2800 2600
Wavenumber (cm-1)
a
b
c
d
Dimer in Ar Matrix
Dimer in a supersonic jet expansion
Dimer in CCl4 solution
N N
H
(7-azaindole)(7-azaindole)22 formation in Ar matrix is probed using infrared spectroscopy formation in Ar matrix is probed using infrared spectroscopy
Mukherjee and Chakraborty, CPL 546 (2012) 74
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Qe NORMAL
S0
S1
Qe TAUTOMER
Q
V(Q
)N N
NN
HH
NN
H
N N
H
N N
NN
HH
NN
H
N N
H
X
DPT of (7-azaindole)DPT of (7-azaindole)22 is inhibited in Ar matrix is inhibited in Ar matrix
Mukherjee and Chakraborty, CPL 546 (2012) 74
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300 400 500
Wavelength (nm)
Inte
nsity ex = 291.5 nm
ex = 310 nm
330
315
338 N N
NN
HH
NN
H
N N
HX
300 400 500
Annealed matrix
Inte
nsity
Wavelength (nm)
DPT of (7-azaindole)DPT of (7-azaindole)22 is inhibited in Ar matrix is inhibited in Ar matrix
3600 3400 3200 3000 2800 2600Wavenumber (cm-1)
d
N N
H
Pre-annealed matrix
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7AICyclic amides
O N
NN
H
HC
Thymine Adenine
7-azaindole∙∙∙amide complexes7-azaindole∙∙∙amide complexes
O
NN
N
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7-azaindole∙∙∙7-azaindole∙∙∙δδ-valerolactum complex-valerolactum complex
(7AIVL)Normal (7AIVL)Tautomer
S0
S1 6.0 kcal/mol
18.5 kcal/mol
~67
.0 k
cal/m
ol
91.7
kca
l/mol
(7AI2)Normal (7AI2)Tautomer
S0
S1 10.0 kcal/mol
14.5 kcal/mol67
.5 k
cal/m
ol
92.2
kca
l/mol
7AI-valerolactam (VL)
Normal form Tautomeric form
CIS/6-311++G**
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Wavelength (nm)
ex = 312 nm
10-5M 7AI10-5M 7AI + 10-3 M VL
12
1
2
7AI+ VL
350 400 450 500 550
0 2000 4000 6000
50
100
150
200
250
Wavelength (nm)
1/[VL]1/
A
Ka = 1.64 103 M-1
7AI+VL
260 280 300 320 340
Efficient tautomeric conversion is observed in hydrocarbon solution at room temperature
Tautomerization of 7-azaindole∙∙∙Tautomerization of 7-azaindole∙∙∙δδ-valerolactum complex-valerolactum complex
Mukherjee et al, JPCA, 2012
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Wavelength (nm)
7AI+VL
260 280 300 320 340
32200 3240032100 32300Wavenumber (cm-1)
22.5
69 76
114.
5
149
137
153
171
prob = total fluorescence
45 92 99
145
000
Wavelength (nm)311.5 310.6 309.6 308.6
Ene
rgy
Reaction Co-ordinate
v = 0v =1v = 2
v = n
v = 0v = 1v = 2
v = n
S0
S1
X
X
Tautomerization of the complex is inhibited under a jet-cooling conditionTautomerization of the complex is inhibited under a jet-cooling condition
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200 300 400 500 600
0
50
100
Wavelength (nm)
T(%
)
22.5
45
114.
5
149
69 76
prob = 300 – 400 nm (local emission)000
32200 3240032100 32300Wavenumber (cm-1)
22.5
69 76
114.
5
149
137
153
171
prob = total fluorescence
45 92 99
145
000
prob = 400 – 750 nm (tautomer emission)
Wavelength (nm)
T(%
)
No tautomeric conversion in jet cooled condition
3205
4 cm
-1
S0
S1
Mukherjee et al, JPCA, 2012
200 300 400 500 600
0
40
80
Wavelength (nm)
UV32+ U330
200 400 600 800
0
40
80
120
Wavelength (nm)
UV+ IR cut filter
Tautomerization of the complex is inhibited under a jet-cooling conditionTautomerization of the complex is inhibited under a jet-cooling condition
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Photophysics of 7-azaindolePhotophysics of 7-azaindolePyrazole complexPyrazole complex
S0
S1
S1
S08.2 kcal/mol
13.4 kcal/mol
99.6 kcal/mol
78.0 kcal.mol
16 kcal/mol
Karmakar and Chakraborty, CPL, 2013
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Tautomerization of 7-azaindoleTautomerization of 7-azaindolePyrazole complex is inhibited in a supersonic jetPyrazole complex is inhibited in a supersonic jet
Karmakar and Chakraborty, CPL, 2013
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Complex vs homodimer Complex vs homodimer
7-azaindole7-azaindolePyrazole complex Pyrazole complex
7-azaindole7-azaindolecyclic amide complex cyclic amide complex
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Concluding remarks Concluding remarks
• Excited state tautomerization of 7-azaindole dimer is easily affected by external perturbations
• Compared to homodimer, the tautomerization barriers of mixed dimeric complexes appear much larger, and further studies are essential to understand the origin.
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Acknowledgement:
Co-workers:
Dr. Moitrayee Mukherjee
Ms. Shreetama Karmakar
Funding:
Department of Science and Technology, Govt. of India