Transcript Chromophores.pptx

Ultrafast Photophysics of Simple Aromatic Chromophores
R. Montero, A. Peralta-Conde, V. Ovejas, M. Fernández-Fernández and Asier Longarte
Facultad de Ciencia y Tecnología
Departamento de Química Física
Universidad del País Vasco/Euskal Herriko Univertsitatea (UPV/EHU)
67th Ohio Spectroscopy Meeting
Aromatic chromophores
S0→Sn
Characterized by strong ππ* transitions that allow an efficient photoexcitation
Provide biomolecules the ability to absorb sun light
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Electronic-Vibrational Coupling
S1
Sn
+
S0
N-H
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Ultrafast Processes Following Phtoexcitation in Molecular Systems
Photophysics (Electronic-vibrational relaxation)
• Intramolecular vibrational redistribution (IVR)
• Internal conversion
• Intersystem Crossing
• Dynamics Trough Conical Intersections
• Wavepacket dynamics
• Electronic coherence
Coherent nature
Essential steps of photochemical reactions that may be tracked in real time
by using femtosecond laser pulses !!!.
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Femtosecond Laser Pulses
Pump-Probe Scheme
Time Resolved Multi Photon Ionization Spectroscopy
Ion
Ion
Aniline S1
Ion
1
S2
Aniline+ (287nm/1305nm)
Ion Signal (a.u)
Probe
Probe
Δt
0.08
0.06
0.04
Ions
Sn
oscillatory component
FFT based fit.
S1
0.02
0.00
-0.02
-0.04
S0
-0.06
0
0
0
500
500
1000
1000
1500
1500
2000
2500
2000
2500
Δt
Time (fs)
Pump
S0
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Experimental Set-up
Pump
AMN-28+
Ion Intensity (a.u.)
Ion Intensity
Ion Intensity
Time of Flight Mass Spectrometer
C2H4+
AMN
4
6
8
10
12
Time of Flight (s)
14
16
Δt
Pump+Probe
Pump0
20
40
60
80
TimeDelay
(ps)
Pump-Probe
100
120
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Experimental Set-up
Femtoseond Laser System 1
3.6 mJ @ 1KHz, 35 fs, 0.1 Terawatt
TOF Spectrometer
1
Femtoseond Laser System 2
4.5 mJ @ 1KHz, 35 fs, 0.13 Terawatt
TOF Spectrometer
1
NOPA 1
NOPA 2
Fluorescence Up-Conversion
NOPA 1
Regenerative Amplifier 4.5
fs
mJSystem
@
1KHz,
Femtoseond Laser
3 2 35
NOPA
40 mJ @ 10Hz, 35
fs, 1.1
Terawatt
0.13
Terawatt
Oscillator
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πσ* States
*A.
L. Sobolewski et al., Phys. Chem. Chem. Phys., 2002, 4, 1093.
Aniline
*A.
*G.
A. Kinget al., J. Chem. Phys. 2010, 132, 214307
Indole
Phenol
Pyrrole
L. Sobolewski et al., Phys. Chem. Chem. Phys., 2002, 4, 1093.
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Indole Photophysics
Electronic Structure
Energy(eV)
1305 nm
S3 πσ*
S1 ππ*
S2 ππ*
S0
*A.
L. Sobolewski et al., Phys. Chem.
Chem. Phys., 2002, 4, 1093–1100
283 nm
243 nm
RN-H
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Indole Photophysics
Transients collected at excitation energies in the region of the Lb and La
states, while probing with 1305 nm
La/S2 ππ*
1
S0
1
269 nm
283 nm
d)
283 nm/1305 nm
Ion Signal
Lb/S1
ππ*
a)
269 nm/1305 nm
=39 12fs
τ1=39±12
 =ns
τ3=ns
τ3=ns

0
0
-200
0
200
400 600
Time (fs)
800
1000 1200
-200
0
200
400
600
800
1000
1200
Time (fs)
RN-H
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Indole Photophysics
Interpretation of time constants
Exc. @ 269 nm and above
τ1=40 fs
τ3=ns
Ultrafast electronic coupling of S1(Lb)/S2(La): τ1=40-20 fs
La/S2 ππ*
La/S2 ππ*
Lb/S1
ππ*
Lb/S1
ππ*
S0
S0
τ1
RN-H
Excitation
RN-H
Relaxation
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Indole Photophysics
Transients collected at excitation wavelenghts shorter 263 nm, where the πσ*
state is expected to appear
a)
260 nm/1305 nm
S3 πσ*
1
b)
Ion Signal
Ion Signal
1
τ1=22±9 fs =22 9fs
 =370 110fs
τ2= 370±110
fs
 =ns
τ3=ns



248 nm/1305 nm
τ1=22±9
fs
=22 9fs
τ2= 460±145
=460 145fsfs

τ3=ps
 =ps

0
500
1000
1500
2000
2500
0
3000
500
1000
Time (fs)
S0
1
243 nm
 =460 145fs

0.70
0.68
0.66
0.64
0
0
0.72
500 1000 1500 2000 2500 3000
1500
2000
2500
3000
Time (fs)
c)
243 nm/1305 nm
RN-H
Ion Signal
260 nm
τ1=22±9 fs=22 9fs
 =435fs
125fs
τ2= 435±125
 =315 50 ps
τ3=ns



0
0
500
1000
1500
2000
2500
3000
Time (fs)
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Indole Photophysics
The Signature of the πσ* State
Exc. @ 263 nm and above
Ultrafast dynamics involving the πσ*: τ2=~400 fs
S3 πσ*
S3 πσ*
τ2
S0
S0
RN-H
Excitation
RN-H
Relaxation
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Indole Photophysics
How does the population reach the πσ* surface??
Direct excitation is not possible due to extremely low oscillator strength.
Coupling to the strong ππ* La excitation.
S3 πσ*
La/S2 ππ*
• The ionization probability from the La and πσ*
states is very similar.
τLa→πσ*??
• The value of τLa→πσ* is very similar to τ1=40-20 fs
and we see a single constant for both processes.
S0
RN-H
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Indole Photophysics
Interpretation of time constants
Long component τ3
Relaxation of the long living S1 (Lb)
La/S2
La/S2 ππ*
ππ*
Lb/S1
ππ*
Lb/S1
ππ*
S0
S0
τ3
RN-H
Excitation
RN-H
Relaxation
67th Ohio Spectroscopy Meeting
Indole Photophysics
Interpretation of time constants
Long time constant: τ3= ps-ns
1
Ion Signal
S0
τ3(260 nm)=7±2
ns nm)=7 2 ns
4(260
τ3(243 nm)= 315±50
4(243 nm)ps
=315 50 ps
τ3(235 nm)=150±20ps

=150 20 ps
Lb/S1 ππ*
τ3
τ3
4(235 nm)
0
0
20
40
60
80
Time (ps)
100
120
140
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Indole Photophysics
Interpretation of time constants
Exc. @ 260 nm and above (region where the three surfaces are present)
La/S2 La/S2
Lb/S1
τ1 ??
τ1
S3 πσ*
τ2
τ3
S0
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Indole Photophysics
Main Aspects of the Study
• The experiments permit to track the evolution of the different relaxation channels of
the system up to nanoseconds, with femtosecond resolution. The photophysics of the
molecule is complex involving several channels.
• In the case of indole the photophysical behaviour is mainly driven by the competence
between the conversion of the formed La excited state toward the Lb and πσ* states.
• The relative energy between the bright ππ* transitions and the πσ* state determines
the photophysics of the chromophore.
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People and Institutions
Grupo de Espectroscopía (UPV/EHU)
Dr. Raúl Montero
Dr. Álvaro Peralta Conde
Virginia Ovejas
Marta Fernández
Prof. Fernando Castaño
Dr. Roberto Martínez
Dr. Maria Nieves Sánchez
Dr. Francisco Bsterretxea
Dr. Carolina Redondo
Dr. José Andrés Fernández
Dr. David Navas
Dr. Emilio Cocinero
Dr. Patricia Ecija
Dr. Rafel Morales
Iker León
Jon Apiñniz
Lorena Miñambres
Antonio Veloso
Estíbaliz Méndez
Roberto Fernández
Imanol Usobiaga
Marta Fernández
Financial Support
Spanish Ministry of Economy and Competitiveness
CTQ and CONSOLIDER –Ingenio 2010
Basque Goverment
UPV/EHU
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