STEADY-STATE AND FEMTOSECOND TIME-RESOLVED OPTICAL SPECTROSCOPIC STUDIES OF PERIDININ DERIVATIVES Nirmalya Chatterjee,1 Robielyn P. Ilagan,1 Kazuyoshi Aoki,2 Shigeo Katsumura2 and Harry A. Frank1 1Department of Chemistry, University of Connecticut, Storrs, CT, 06269-3060, USA 2Department of Chemistry, Kwansei Gakuin University, 669-1337, Hyogo, Japan
0.4
0.0
0.0 300
400
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400
Wavelength (nm)
Results
H H3C
ex 1-T
0.6 0.4 0.2
PerAcEs 384 nm 413 nm 433 nm 450 nm
0.4 0.2
0.0 300
350
400
450
500
550
600
CH3
H3C
O HO
CH3
OH
O
H
H3C
CH3
H3C
CH3
CH3
O
all-trans-peridinin
HO
CH3
9.026 min
0.005
ab
B
0.000
0.000
300 0.010
C
400
500
600
300 0.04
C
9.913 min
400
D
500
600
10.275 min
80 fs 540 fs 2 ps 10.4 ps
-4
0.00
0.00
0.000
8
9
10
11
Time (mins)
12
300
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300
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500
Wavelength (nm)
Figure 2. HPLC chromatogram and absorption spectra of 13,14-cis-PerAcEs monitored at 410 nm using a C30 column. Isocratic elution with acetonitrile: methanol:water (87:10:3 v/v/v) at a 0.5 mL/min flow rate.
600
500
600
Wavelength (nm)
4 2
3
C 13,14-cis-PerAcEs probe λ: 520 nm
4
2
D 13,14-cis-PerAcEs probe λ: 630 nm
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1
0
0
0.4
50
100
Time (ps)
150
0
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Time (ps)
150
Figure 10. Transient absorption kinetics at the maximum of the S1 → Sn and SICT → Sn bands (A and B) of peridinin and (C and D) of 13,14-cis-PerAcEs in methanol.
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Wavelength (nm)
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500
600
Summary of observations s The absorption maximum of 13,14-cis-PerAcEs is blue-shifted by ~60 nm compared to that of peridinin, and unlike peridinin shows no solvent dependance. s The fluorescence spectrum of 13,14-cis-PerAcEs is broad and has a maximum at ~690 nm similar to peridinin. s The transient absorption spectrum of 13.14-cis-PerAcEs in methanol shows two peaks at 520 nm and 630 nm that build up at different times. s The S1/ICT lifetime of 13,14-cis-PerAcEs in methanol is ~43 ps which is four times longer than that of peridinin.
Reference
80 fs 540 fs 2 ps 10.4 ps
-4 700
peridinin probe λ: 589 nm
6
0
4
0
800
B
8
0
6
0.6
PerAcEs
4
700
Wavelength (nm)
-2
PerAcEs RT 77 K
0.8
A
Peridinin
0.02
0.005
800
Figure 7. Absorption spectra of 13,14-cis PerAcEs in EPA (ether:isopentane:ethanol 5:5:2 v/v/v) at room temperature (RT) and 77 K.
0.005
∆A/10
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A B
ic
9.307 min
8
0.03
Absorbance
Absorbance
S1/ICT
S0 0.010
A
0.04
0.01
ta
Figure 6. Energy level diagram of the low-lying singlet states of carotenoids. (ic) internal conversion (ab) absorption; (ta) transient absorption (ICT) intramolecular charge transfer.
0.010
D
750
1.0
CH3
0.05
700
Figure 5. Fluorescence spectra of 13,14cis-PerAcEs in methanol excited at different wavelengths. The spectra were normalized at the λmax..
Sn
13,14-cis-PerAcEs
Figure 1. Structures of peridinin and 13,14-cis-PerAcEs.
650
Wavelength (nm)
Figure 4. Fluorescence excitation (ex) (690 nm detection) and 1-T (T is transmittance) spectra of 13,14-cis-PerAcEs in methanol. The spectra were normalized at the λmax.
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0
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peridinin probe λ: 524 nm
2 0.6
313 fs 5.8 ps 43 ps
-1
A
0.8
Intensity
Intensity
0.8
-3
O
600
1.0
PerAcEs
0
Figure 9. Evolution Associated Difference Spectra (EADS) of (A) peridinin and (B) 13,14-cis-PerAcEs in methanol.
∆A/10-3
1.0
S2
OH
500
4
∆A/10
CH3
O
H3C
-0.6
PerAcEs
1
Wavelength (nm)
Figure 3. Absorption spectra of peridinin and 13,14-cis-PerAcEs in (A) n-hexane and (B) methanol at room temperature.
-3
H3C
OCOCH 3
HO
O
CH3
H3C
H3C
600
∆A/10-3
s Examine the effect of the structural changes on the spectral properties s Elucidate the factors controlling the dynamics of the excited states of peridinin and peridinin derivatives
500
Wavelength (nm)
Absorbance
To perform systematic modifications to the structure of peridinin in order to:
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< 130 fs 1 ps 10 ps 30 ps
Wavelength (nm)
Objective
2
-3 ∆A/10
0.6
C D
0.2
0.2
3
∆A/10-3
0.4
0.8
peridinin
∆A/10-3
0.6
in methanol
-3 ∆A/10
Absorbance
Absorbance
0.8
AB→
→
PerAcEs in n-hexane
B
peridinin PerAcEs
1.0
→
Peridinin is a highly substituted carotenoid characteristic of the Peridiniales group of dinoflagellates whose structure features an unusual C37 carbon skeleton rather than the typical C40 system present in most carotenoids. One of its most surprising properties is the fact that the lifetime of the lowest excited singlet state is strongly dependent on solvent environment ranging from 7 ps in the strongly polar solvent, trifluoroethanol, to 172 ps in the nonpolar solvents, cyclohexane and benzene.1 This behavior is highly anomalous for carotenoids which generally show very little dependence of their S1 spectral properties and lifetimes on solvent environment. The findings suggest that the environment of protein-bound peridinin may modulate its light-harvesting efficiency in vivo. This study is aimed at uncovering the molecular features of peridinin that control its excited state properties and dynamics. We have begun an investigation of synthetically-modified peridinins and report here our findings on 13,14-cis-PerAcEs compared to natural peridinin. The spectroscopic properties and dynamic behavior of HPLC-purified 13,14-cis-PerAcEs in methanol and hexane were studied by steady-state absorption, fluorescence, fluorescence excitation, and transient absorption spectroscopy at room temperature. Low temperature (77K) absorption and fluorescence experiments of 13,14-cis-PerAcEs in EPA (5:5:2 v/v/v ether: isopentane: ethanol, EPA) were also done. The investigation shows differences in absorbance maximum, vibrational structure, fluorescence emission maximum and dynamics compared to natural peridinin. The data will be discussed in terms of specific structural features that control the spectroscopic and dynamic behavior of peridinin.
A
peridinin
1.0
→
Abstract
0.6
700
Wavelength (nm)
Figure 8. Transient absorption spectra of (A) peridinin and (B) 13,14-cis-PerAcEs in methanol at different delay times. Excitation wavelength was 490 nm for perdinin and 400 nm for 13,14-cis-PerAcEs.
1. Bautista, J. A.; Connors, R. E.; Raju, B. B.; Hiller, R. H.; Sharples, F. P.; Gosztala, D.; Wasielewski, M. R.; Frank, H. A. J. Phys. Chem. B 1999, 103, 8751.
Acknowledgments This work is supported by grants from the National Institutes of Health (GM-30353) and the University of Connecticut Research Foundation.
