excited state isomerization of a stilbene analog: phenylvinylacetylene josh j. newby, christian w....
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Excited State Isomerization of a Stilbene
Analog: Phenylvinylacetylene Josh J. Newby, Christian W. Müller, Ching-Ping Liu, Hsiupu D. Lee and Timothy S. Zwier
64th International Symposium on Molecular SpectroscopyMF03
Department of Chemistry, Purdue UniversityWest Lafayette, IN 47907
Interest in Phenylvinylacetylene (PVA)
0 200 400 600 800 1000 1200 1400 1600
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.000
0
Flu
ore
scen
ce in
tensi
ty [a
rb. u
nits
]
Relative wavenumber [cm–1]
480
289
330
1105
470
1480
1133
480
4186
320
1231
310
1373
300
1479
280
1 (6b0
1)
624
280
1480
2714
260
1 (10
1)
851
260
1480
2941
250
1 (120
1)
1011
230
11048
250
1480
21100
190
1 (130
1)
1219
180
11283
-90 -60 -30 0 30 60 90 120 150 180 210 240 270
0
100
200
300
400
500
600
700
800
900
1000
V(
) [c
m–1]
Torsional angle
J. Phys. Chem. A 106 (24): 5789-5796 (2002)
J. Phys. Chem. A, 112(39), 9454 (2008)
E-PVA
Inte
nsi
ty /
(ar
b.
un
its)
12008004000Wavenumbers (cm
-1)
482
0
472
0 321
031
10
291
0
290
1
310
1
480
2 470
2
320
1
240
1
200
1
TB02Excitation and Emission Spectroscopy
Z-PVA
Inte
nsity
/ (a
rb. u
nits
)
12008004000Wavenumbers (cm
-1)
Inte
nsity
/ (a
rb. u
nits
)
2000150010005000Wavenumbers (cm
-1)
Fluorescence and Absorbance
UVD(absorption)
LIF(fluorescence)
LIF(fluorescence)
UVD(absorption)
Indicates the turn on of a fast, non-radiative process
1000 cm-1 600 cm-1
Relative Wavenumbers (cm-1)Relative Wavenumbers (cm-1)
E/Z Isomerization
1A (S0)
1B (S1)
2A (S2)
trans (E) cis (Z)
1A´ (S0)
1A′ (S1)
2A″ (S2)
trans (E) cis (Z)
?
Is the loss in fluorescence due to cis/trans isomerization?
UV PUMP
To diffusion pump
UV Probe
Reaction Channel
Rxn quenched by expansion on s
timescales
Pulsed Valve
Pump Probe
60-80s
hν
hν hν
Ultraviolet Population Transfer (UVPT) in a time-of-flight mass spectrometer
TOF into plane
Determine product distribution via R2PI
spectroscopy
?
Reaction channel constrains the expansion allowing us to remove large amounts of
internal energy from molecules.
Expt’l protocol:1. Cool2. Pump3. Re-cool4. Probe
Ultraviolet Population Transfer (UVPT)
S1
Z-PVA S0
S1
E-PVA S0
kiso
kIC
Pu
mp
Pro
be
Coo
lk´iso
Hole-filling spectroscopy: Fix Pump, Tune Probe: See where the population went
Population transfer spectroscopy: Tune Pump, Probe on E Watch population come into E from Z Z
Z
ZZ
Z
EE
ZZ*Z Z
E* E*ZZ Z
Cool
EXCITE COOL PROBE
Z*
Z
COOL
Infrared-Population Transfer SpectroscopyInfrared-Population Transfer Spectroscopy
WG13
J. Phys. Chem. A., 110 (12), 4133 (2006)
J. Chem. Phys., 120 (1), 133 (2004)
J. Chem. Phys., 120 (19), 9033 (2004)
William H. James III
E-PVA Population Transfer Spectra
Inte
nsity
/ (a
rb. u
nits
)
12001000800600Relative Wavenumber / (cm
-1)
Inte
nsity
/ (a
rb. u
nits
)
12008004000Relative Wavenumbers / (cm
-1)
E → Z
E → E
UVD
E → Z
E → E
Scan Pump, Probe Z Measures population moved into a product well.
Scan Pump, Probe EMeasures how much population escapes the reactant well under collisional conditions
UVDMeasures how much population can be removed from the reactant well under “zero” collisional conditions
Z-PVA Population Transfer Spectra
Inte
nsity
/ (a
rb. u
nits
)
12001000800600Relative Wavenumber / (cm
-1)
Inte
nsity
/ (a
rb. u
nits
)
12008004000Relative Wavenumbers / (cm
-1)
E → Z
E → E
Z → E
hot bands
Scan Pump, Probe E Measures population moved into a product well.
Scan Pump, Probe ZMeasures how much population escapes the reactant well under collisional conditions
UVDMeasures how much population can be removed from the reactant well under “zero” collisional conditions
Z → Z
UVD
Isomerization Quantum Yields
Δν/cm-1 Φrf (E)a Φr
EZ Δν/cm-1 Φr
f (Z)b ΦrZE
0 1.00 1.00 538 0.30 1.00
326 0.67 0.77±0.23 702 0.02 1.46±0.44
815 0.90 0.90±0.27 937 0.02 0.95±0.29
931 1.26 0.86±0.26 967 0.03 1.59±0.48
1214 0.19 0.96±0.29 1060 0.01 1.54±0.46
1279 0.18 0.77±0.23 1152 0.02 1.05±0.32
1292 0.13 0.81±0.24 1223 0.02 1.19±0.36
1434 0.11 0.61±0.18
Take home: Isomerization is not the cause of the loss in fluorescence!
(a) FL Quantum Yields relative to E-PVA 000
(b) FL Quantum Yields relative to Z-PVA 000
0 20 40 60 80 100 120 140 160 180
0
5000
10000
15000
20000
25000 CIS/6-311+G(d,p)
V(
) [c
m–1
]
Torsion angle [ °]
CIS/6-311+G(d,p)
CASSCF(10,10)/6-31G(d)
S1
S2
kink
Double Bond Torsional PES
Inte
nsity
/ (a
rb. u
nits
)
12008004000Wavenumbers (cm
-1)
Inte
nsity
/ (a
rb. u
nits
)
2000150010005000Wavenumbers (cm
-1)
Fluorescence and Absorbance
UVD(absorption)
LIF(fluorescence)
LIF(fluorescence)
UVD(absorption)
What is the non-radiative process?
Relative Wavenumbers (cm-1) Relative Wavenumbers (cm-1)
PVA Excited States
0
1
2
3
4
5
6
7
8
-80 -40 0 40 80
ZPVA
0
1
2
3
4
5
6
7
8
-80 -40 0 40 80
EPVA
Angle (°) Angle (°)
Rel
ativ
e E
nerg
y (e
V)
Rel
ativ
e E
nerg
y (e
V)
1A′
2A′
3A′
2A′
3A′
1A″
2A″2A″
1A″
1A′
π→π*
π→σ*
π→σ*
π→π*
Close lying A″ states in both E and Z-PVA which correspond to the π→σ*excitation
Excited States Cont.
M. Z. Zgierski and E. C. Lim Chem. Phys. Lett. 387 352 2004
T. Fujiwara, M. Z. Zgierski, and E. C. Lim, JPCA 112, 4736 2008
1,4-Bis(phenylethynyl)benzene
Conclusions• UVPT has been developed to elucidate excited state
dynamics
• E/Z Isomerization does NOT dominate in the excited state
• Isomerization most likely occurs on the ground state surface after interconversion
• PVA most likely departs initially excited A´ state to an A″ state via intersection
• No isomerization channel to naphthalene was observed
AcknowledgementsProfessor Timothy S. Zwier
The Zwier GroupWilliam James WG13Chirantha Rodrigo MF05 Josh Sebree TB03Evan Buchanan TB09Zachary DavisJames RedwineRyan MuirDeepali MehtaDr. Jaime StearnsDr. Talitha SelbyDr. Jasper ClarksonDr. V. Alvin ShubertDr. Esteban BaqueroDr. Tracy LeGreveDr. Nathan PillsburyDr. Ching-Ping LiuDr. Christian Müller MF06, TB10Dr. Mike Nix
PVA Excited States
π→σ*
π→π *
A″A′
π→σ*
π→π *
A′A″
1.50 1.50
1.00 1.00
0.50 0.50
0 0
Inte
nsity
/ (a
rb. u
nits
)
2000150010005000Wavenumbers (cm
-1)
Fluorescence Quantum Yields
1.00 1.00
0.75 0.75
0.50 0.50
0.25 0.25
0.00 0.00
Inte
nsity
/ (a
rb. u
nits
)
120010008006004002000Wavenumbers (cm
-1)
Φr f
Φr f
(b)
(a)
Relative Wavenumbers (cm-1)
Relative Wavenumbers (cm-1)
Inte
nsity
/ (a
rb. u
nits
)
12008004000Wavenumber / (cm
-1)
x100
PVA PT compared to LIF
Inte
nsit
y / (
arb.
uni
ts)
12008004000
Wavenumbers / (cm-1
)
x4 x40
Isomerization is not the non-radiative feature that dominates.
Relative Wavenumbers (cm-1) Relative Wavenumbers (cm-1)
PVA fluorescence spectroscopy
Loss in fluorescence but still show Frank-Condon Factors
Isomerization? Internal Conversion? Intersystem Crossing?
Inte
nsity
/ (a
rb. u
nits
)
12008004000Relative Wavenumber / (cm
-1)
Inte
nsity
/ (a
rb. u
nits
)
12008004000Relative Wavenumbers / (cm
-1)
000
000
000
000
2510
2610 191
0
2601
2501
1901
2401
2901
2910
2001
(a)(b)
LIF LIF
SVLF SVLF
000+ 1000 cm-1 00
0+ 600 cm-1
Inte
nsit
y (A
rbit
rary
Uni
ts)
35000348003460034400342003400033800
Wavenumbers (cm-1
)
UVPT of Z-PVA to E-PVA
1184
X 50TUNE Pump
Probe E-PVA 000
LIF of Z-PVA
UVPT of Z to E
‘Gain’ E-PVA population when
resonant with a Z-PVA transition.
Tdnvib~15 K
Many hot bands of Z-PVA observed.
000
0284
2084
2284
1031
3184
(6b) 2810
(12) 2410
Tupvib~50 K
Hole-filling of PVA Z to E and E to Z
Inte
nsit
y (A
rbit
rary
Uni
ts)
345003400033500Wavenumbers (cm
-1)
Inte
nsit
y (A
rbit
rary
Uni
ts)
34100340003390033800337003360033500Wavenumbers (cm
-1)
LIF of E-PVA LIF of Z-PVA Hole-filling Z to E
LIF of E-PVA LIF of Z-PVA Hole-filling E to Z
Pump Z PVA 000 +933 cm-1 TUNE Probe Pump E PVA 00
0 +931 cm-1 TUNE Probe