Resonance energy transfer from a dye molecule

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Resonance energy transfer from a dye molecule to
Nanotubes and Layers
R. S. Swathi 24/03/08
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Contents of the talk
-Resonance energy transfer (RET)
Why worry about it??
-RET from dyes to nanotubes
-RET from dyes to graphene
Our results
-Future directions
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Resonance Energy Transfer (RET)
Donor
Acceptor
coulombic interaction
Animation obtained with permission from Dr.
Rolands animations on FRET
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When the donor is fluorescent,
Fluorescence Resonance Energy Transfer (FRET)
Forsters Observation (1946)
Rate of transfer - a very strong function of the
distance between the donor and the acceptor!!
Forster radius
Spectral overlap
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Interacting transition dipole moments
Interaction energy
Molecular Fluorescence by Bernard Valeur,
Wiley-VCH
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Energy transfer efficiency
Transfer efficiency
Steady state method
Time resolved method
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Classic experiments by Stryer, 1967
Since then, a spectroscopic ruler in studying
biological conformational dynamics
effective in the range
Acceptor
Donor
Schuler et. al. Nature, 419, 743 (2002)
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In FRET,
Donor
Dyes
Acceptor
Recent interest
Variety of materials like nanoparticles,
nanotubes, quantum dots, quantum wells .........
Strouse et. al. JACS 127,3115 (2005)
Qu et. al. J. Chem. Phys. 117, 8089 (2002)
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RET from dyes to nanotubes
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Nanotubes as energy acceptors
Why nanotubes are interesting??
nanotubes functionalized with biomolecules like
proteins, lipids. are useful for transporting
them across cell membranes
Lipid molecules labelled with dyes assembled onto
a nanotube
Fluorescence quenching and recovery
Evidence for biomolecular transport
Lin et. al. APL 89,143118 (2006)
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Nanotube-dye interactions are of fundamental
importance
Development of various synthetic strategies
for functionalizing nanotubes with dyes.
1) Tethering the outer surface of the
nanotube with the dye
2) Encapsulating the dye within the nanotube
-terminal functionalisation -sidewall
functionalisation
non-covalent interactions
covalent interactions non-covalent interactions
interactions
Yanagi et. al. JACS 129,4992 (2007)
Alvaro et. al. CPL 384,119 (2004)
Martin et. al. JPCB 108,11447 (2004)
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Our interest
nanotubes covalently functionalized onto the
sidewalls with a dye.
Dye
pyrene
Excited electronic states are long-lived (150ns)
Ideal probes for studying interactions with
nanotubes
Li et. al. Journal of Photochemistry and
Photobiology A 185, 94 (2007)
Qu et. al. J. Chem. Phys. 117, 8089 (2002)
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Scheme of functionalization
Ipy
Monofunctionalized pyrene
Qu et. al. J. Chem. Phys. 117, 8089 (2002)
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Absorption and Emission spectra in solution
Ipy
Ipy-nanotube
Ipy
Intensity
Absorption 340 nm
Emission 390 nm
Ipy-nanotube
Wavelength (nm)
New emission band 490 nm
Absorption spectra
No ground state complexation between Ipy and
nanotube
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Broadening of the bands of Ipy on attachment to
nanotube!
Heterogeneous environment on the nanotube surface
Excimer formation on tethering to the nanotube
(Excited state dimer)
Fluorescence spectra are independent of solution
conc.
Excimer formation is intramolecular (on the same
nanotube)
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Time resolved fluorescence studies in solution
For Ipy,
Fluorescence decay single exponential
For Ipy-nanotube,
Intensity
Decay for both monomer and excimer
multi-exponential
Monomer decay is much faster on functionalization
Quenching of monomer excited state
Time (ns)
Excimer formation??
Excitation energy transfer to nanotube??
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The goal is to understand dye-nanotube
interactions!!
Avoid complication due to excimer formation??
Absorption and Emission spectra in polymer matrix
IPy
IPy-nanotube
Excimer emission is suppressed to a great extent
Intensity
Single emission band simplifies the study of
Ipy-nanotube interaction
Wavelength (nm)
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Time resolved fluorescence studies in matrix
Monomer decay is much faster despite no
excimer formation
Energy transfer from pyrene to the nanotube
is responsible for quenching
Intensity
Fluorescence of the dyes can be quenched by
the nanotubes!!!
Time (ns)
Qu et. al. J. Chem. Phys. 117, 8089 (2002)
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Effect of tether length on energy transfer
Rate of energy transfer depends on the
distance between the dye and the nanotube
Longer tether more flexible pyrene moieties
more favorable for excimer formation less
favorable for energy transfer
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n1 Ipy n4 Ipy
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Decay monitored at 390nm for Ipy-nanotube
Fluorescence is long-lived in polymer matrix
than in solution
due to suppression of excimer formation
excimer formation is more favorable than energy
transfer in solution
Effect of longer tether!!!
Evidence for the mechanism of quenching
Martin et. al. JPCB, 108, 11447 (2004)
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Fluorescence quantum yields
Ipy 0.35
Ipy - 0.63
Ipy-nanotube - 0.07
Ipy-nanotube 0.27
Compare the relative quantum yields??
Rate of fluorescence quenching is high for Ipy
than for Ipy.
The tether length is crucial in determining the
rate of fluorescence quenching!!!
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Conclusions
nanotube-dye interactions are of fundamental
importance for a wide range of applications.
Steady state and time resolved fluorescence
experiments reveal quenching of the pyrene
excited states as a result of excimer formation
and energy transfer to nanotubes.
Tether length plays a crucial role in determining
the mechanism of fluorescence quenching.
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RET from dyes to graphene
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Graphene, new promising material
Graphite
A single layer of graphite, graphene
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Imagine the nanotube to be a rolled up sheet of
graphene
Animation from S. Maruyamas carbon nanotube site
Graphene is the starting point for all
theoretical calculations on graphite, carbon
nanotubes and fullerenes!!!
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RET from a vibrating dipole to a metal surface
metal
??
Electron-hole pair excitations in metal
Persson and Lang, PRB, 26, 5409 (1982)
Transfer to a 2D array of dipoles
Experimental verification!!!
Alivisatos et. al. JCP, 82, 541 (1985)
Ryberg PRB, 32, 2671 (1985)
Infrared lifetime measurements
Infrared life
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We think of energy transfer to graphene!!!
No experiments available!!!
What is the distance dependence of rate for
graphene???
Energy transfer to a 2D array of point dipoles
We expect it to be z-4 !
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The graphene lattice
The unit cell is a parallelogram
The lattice is made up of 2 types of carbon atoms
Carbon 2pz wavefunction
Determine the expansion coefficients variationally
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interesting electronic properties of graphene!!
The Fermi level is a set of six points, the
K-points
Near the K-points,
linear dispersion relation
Energy band structure
Theoretically fascinating !!!!
P R Wallace, Phys. Rev. 71, 622 (1947)
Katsnelson, Mat. Today. 10, 20 (2007)
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Understanding the interaction between dye and
graphene!!
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Rate of energy transfer to graphene
emission energy of the dye
The leading term in the rate of transfer is
where
Yukawa type dependence ( ) of the rate on
the distance
Why Yukawa type distance dependence?
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Results
for pyrene
for a near IR emitting dye
Quenching is efficient upto 40 Å for pyrene and
upto 70 Å for the near IR emitting dye.
Swathi and Sebastian (submitted)
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Conclusions
The rate of energy transfer from a dye molecule
to graphene has a Yukawa type dependence on the
distance.
We believe that our calculations would provide
motivation for carrying out energy transfer
measurements from molecular excited states to
graphene.
What next??
Graphene as energy donor in RET
Distance dependence of the rate of transfer to
nanotubes!!
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Thank You
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Intensity
Time (ns)
solution spectra
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Time resolved fluorescence studies
Intensity
Intensity
Time (ns)
Time (ns)
Faster decays of both monomer and excimer
emissions on tethering
Consistent with low overall quantum yields
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Alternative means to avoid excimer formation??
2
1
Use 1 and 2 in different ratios to alter the
content of pyrene on the nanotubes
I 13 ratio
pyrene content
II 19 ratio
IgtIIgtIII
III 115 ratio
Li et. al. Journal of Photochemistry and
Photobiology A 185, 94 (2007)
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Fluorescence spectra in solution
I
II
III
Intensity
Quantum yields
Free pyrenemethanol 0.67
Wavelength (nm)
I 0.15
II 0.13
III 0.07
Significant quenching of fluorescence due to
energy transfer to the nanotube
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Time resolved fluorescence studies in solution
Lifetime of free pyrenemethanol 300ns
For emission at 390nm, average lifetimes of I-III
are all about 70ns
Rate of energy transfer is much higher than that
of excimer formation
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For emission at 490nm, average lifetime is
progressively shorter from I to III
I 58ns
II 34ns
III 19ns
Li et. al. Journal of Photochemistry and
Photobiology A 185, 94 (2007)
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