5 research outputs found
Organization of Bacteriochlorophylls in Individual Chlorosomes from Chlorobaculum tepidum Studied by 2-Dimensional Polarization Fluorescence Microscopy
Chlorosomes are the largest and most efficient natural light-harvesting systems and contain supramolecular assemblies of bacteriochlorophylls that are organized without proteins. Despite a recent structure determination for chlorosomes from Chlorobaculum tepidum (Ganapathy Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 8525), the issue of a possible large structural disorder is still discussed controversially. We have studied individual chlorosomes prepared under very carefully controlled growth condition by a novel 2-dimensional polarization single molecule imaging technique giving polarization information for both fluorescence excitation and emission simultaneously. Contrary to the existing literature data, the polarization degree or modulation depth (<i>M</i>) for both excitation (absorption) and emission (fluorescence) showed extremely narrow distributions. The fluorescence was always highly polarized with <i>M</i> ≈ 0.77, independent of the excitation wavelength. Moreover, the fluorescence spectra of individual chlorosomes were identical within the error limits. These results lead us to conclude that all chlorosomes possess the same type of internal organization in terms of the arrangement of the bacteriochlorophyll c transition dipole moments and their total excitonic transition dipole possess a cylindrical symmetry in agreement with the previously suggested concentric multitubular chlorophyll aggregate organization (Ganapathy Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 8525<i>)</i>
Single Lévy States–Disorder Induced Energy Funnels in Molecular Aggregates
Using
fluorescence super-resolution microscopy we studied simultaneous spectral,
spatial localization, and blinking behavior of individual 1D J-aggregates.
Excitons migrating 100 nm are funneled to a trap appearing as an additional
red-shifted blinking fluorescence band. We propose that the trap is
a Frenkel exciton state formed much below the main exciton band edge
due to an environmentally induced heavy-tailed Lévy disorder.
This points to disorder engineering as a new avenue in controlling
light-harvesting in molecular ensemble
Polarization Imaging of Emissive Charge Transfer States in Polymer/Fullerene Blends
Photoexcitation of conjugated polymer–fullerene
blends results
in population of a local charge transfer (CT) state at the interface
between the two materials. The competition between recombination and
dissociation of this interfacial state limits the generation of fully
separated free charges. Therefore, a detailed understanding of the
CT states is critical for building a comprehensive picture of the
organic solar cells operation. We applied a new fluorescence microscopy
method called two-dimensional polarization imaging to gain insight
into the orientation of the transition dipole moments of the CT states,
and the associated excitation energy transfer processes in TQ1:PCBM
blend films. The polymer phase was oriented mechanically to relate
the polymer dipole moment orientation to that of the CT states. CT
state formation was observed to be much faster than energy transfer
in the polymer phase. However, after being formed an emissive CT state
does not exchange excitation energy with other CT states, suggesting
that they are spatially and/or energetically isolated. We found that
the quantum yield of the CT emission is smaller for CT states spatially
located in the highly oriented polymer domains, which is interpreted
as the result of enhanced CT state dissociation in highly ordered
structures