Plenarvorträge - DPG-Tagungen

Chemische Physik und Polymerphysik Montag
CPP 9 Single Molecule Spectroscopy
Zeit: Montag 14:00–15:30 Raum: H 38
CPP 9.1 Mo 14:00 H 38
Controlled Fluorescence Bursts from Single Conjugated Polymers
induced by Triplet Quenching — •Florian Schindler 1 ,
John M. Lupton 1 , Ullrich Scherf 2 , and Jochen Feldmann 1 —
1 Photonics and Optoelectronics Group, Sektion Physik, LMU Munich —
2 FB Chemie, University Wuppertal
Single molecule spectroscopy provides fundamental insight into the
nature of emission from conjugated polymers. Triplet excitons are particularly
important in these materials. We demonstrate here that triplet
quenching by molecular oxygen can lead to dramatic fluorescence bursts
from conjugated polymers before photo-oxidation sets in. The fluorescence
burst is imaged in single molecules of a comparatively photostable
ladder-type poly(para-phenylene). Triplet shelving is identified as an important
mechanism limiting the fluorescence yield of conjugated polymers
due to both a reduction in photon cycling rates and singlet-triplet quenching
in the multichromophoric system. The fact that triplet quenching
clearly enhances the fluorescence intensity from polymers suggests that
intramolecular energy transfer of singlet excitons to long-lived triplet
states generated simultaneously on a single polymer chain can also form
a quenching pathway for singlet excitons. Besides enabling a direct monitoring
of oxygen diffusion through thin polymer films, the sudden fluorescence
burst provides a novel tool to study the properties of triplet
excitons in conjugated polymers at room temperature down to the single
molecule level.
CPP 9.2 Mo 14:15 H 38
Single molecule spectroscopy at cryogenic temperatures using
vibronic excitation and dispersed fluorescence detection
— •Alper Kiraz, Moritz Ehrl, Christoph Bräuchle, and Andreas
Zumbusch — Department Chemie, Ludwig-Maximilians Universität
München, Butenandtstr. 11, D-81377 München, Germany
Low temperature single molecule spectroscopy experiments often rely
on excitation from the purely electronic zero-phonon-line and collecting
the Stokes shifted fluorescence[1]. A major problem of this technique
however, is that only exceptionally photostable systems can be studied.
Because the absorbing zero-phonon-line is so narrow, already small spectral
jumps (>30 GHz) in absorption lead to a loss of the excitation.
Here we report vibronic excitation combined with spectrally resolved
zero-phonon-line detection as a novel technique for single molecule spectroscopy
at cryogenic temperatures. In contrast to zero-phonon-line excitation,
vibronic excitation benefits from large absorption bands (broadened
by 1-10 ps lifetimes and phonon sidebands) allowing for investigation
of large spectral jumps. We observed single terrylenediimide molecules
in both n-hexadecane (Shpol’skii matrix) and PMMA (polymer), and
recorded spectral jumps as large as 80 cm −1 with 1 sec time resolution[2].
This technique promises applications in spectroscopy of a wide-range of
single molecules in amorphous hosts including fluorescing proteins. It also
allows for investigation of the emission linewidth of a single molecule’s
zero-phonon-line.
[1] A.-M. Boiron et al., Chem. Phys. 247, 119 (1999).
[2] A. Kiraz et al., J. Chem. Phys. 118, 10821 (2003).
CPP 9.3 Mo 14:30 H 38
Single Molecule Diffusion in Nanostructured Molecular Sieves
— •Johanna Kirstein 1 , Christian Hellriegel 1 , Christoph
Bräuchle 1 , Peter Behrens 2 , Nikolay Petkov 1 , and Thomas
Bein 1 — 1 LMU München, Dept. Chemie, Butenandtstr. 11, 81377
München — 2 Universität Hannover, Callinstr. 9, 30167 Hannover
Single molecule spectroscopy (SMS) is used to characterise diffusion
in nanometre sized structures. Here we show the diffusion of single TDI
molecules incorporated as guests into the pores of a M41S-host using
single particle tracking (SPT). A major advantage of SPT compared to
e.g. FCS is the possibility to obtain the trajectory of a fluorescent dye
molecule.
This has been demonstrated recently for TDI molecules diffusing in
monoliths of M41S using confocal microscopy. New studies in similar,
spincoated samples using wide field imaging provide an improved temporal
resolution. X-Ray diffraction measurements will point out the existence
of a hexagonal or cubic order of the pores in an otherwise amorphous
solid body. With SPT we obtain structured trajectories, which
reflect the tortuosity of the channels. These trajectories help to understand
better the channel structure of the hosts and the influence of the
pores on the diffusional behaviour of the guest molecules.
CPP 9.4 Mo 14:45 H 38
Orientation of Single Molecules in Nanostructured Molecular
Sieves — •Christian Hellriegel, Christian Seebacher,
Christophe Jung, and Christoph Bräuchle — LMU München,
Dept. Chemie, Butenandtstr. 11, 81377 München
Revealing heterogeneities and measuring the distribution of a physical
property of a system is a major advantage of single molecule spectroscopy
(SMS) compared to conventional ensemble methods. Recently we have
shown that single fluorescent dye molecules can also be detected if the
molecules are incorporated as guests in inorganic molecular sieves. Furthermore,
it is possible to obtain the molecule’s emission spectrum and
to determine its orientation using a confocal setup.
In the presented study we examine the influence of molecular size
on the orientational distribution: Three differently sized Oxazine dye
molecules have been incorporated during synthesis into AlPO4-5 crystals
(unidimensional channels, pore diameter 760pm). By analysing the
orientation of many individual molecules with respect to the channel axis,
we determine the effect of the molecular size on the orientational distribution,
and to which extent the host’s structure influences the alignment
of the molecules. During the measurements we also observe spectral dynamic
events, and in rare cases orientational jumps.
CPP 9.5 Mo 15:00 H 38
Single Molecule Microscopy of Aligned Molecules in a Thin
Crystalline Film — •Robert Pfab, Jan Zimmermann, Christian
Hettich, Ilja Gerhardt, Alois Renn, and Vahid Sandoghdar
— Physical Chemistry Laboratory, Swiss Federal Institute of Technology
(ETH), CH-8093 Zurich, Switzerland
Thin films of terrylene doped para-terphenyl have been fabricated
and characterised with optical microscopy, AFM measurements and single
molecule microscopy. Individual terrylene molecules are found to be
aligned with their transition dipole moment perpendicular to the plane
of the film, as observed by their characteristic dipole emission patterns.
The fluorophores are shown to be extremely photochemically stable. The
homogeneity of the film makes such samples ideal for scanning probe microscopy
techniques, and the orientation of the molecules provide a well
defined system for studying dipole-dipole interactions.
CPP 9.6 Mo 15:15 H 38
Optical Polarization Tomography: A new method to determine
the three-dimensional orientation of single molecules
— •Michael Prummer 1 , Horst Vogel 1 , Beate Sick 2 , Bert
Hecht 3 , and Urs P. Wild 4 — 1 Institute of Biomolecular Sciences,
EPFL, CH-1015 Lausanne — 2 DNA-Array Facility, University of Lausanne,
CH-1015 Lausanne — 3 Institute of Physics, University of Basel,
CH-4056 Basel — 4 Physical Chemistry Laboratory, ETH-Hönggerberg,
CH-8093 Zürich
We apply the concept of tomography to polarization-sensitive optical
microscopy of single fluorophores to determine the three-dimensional
orientation of molecular absorption dipoles with isotropic sensitivity.
Wide-field microscopy provides the opportunity to monitor simultaneously
three-dimensional rotation and two-dimensional translation of
many molecules in parallel. For orientation determination the molecules
are illuminated from different directions of incidence with linearly polarized
light. In each exposure the excitation along a particular projection of
the absorption dipole on the electric field leads to a distinct fluorescence
intensity. Five exposures are sufficient to determine the full orientation
of the fluorophores.