Investigation of molecular dimers by ensemble and single molecule spectroscopy

Abstract

Investigation of molecular dimers by ensemble and single molecule spectroscopy Christ, Th.; Petzke, F.; Bordat, P.; Herrmann, Andreas; Reuther, E.; Müllen, K.; Basché, Th. Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Christ, T., Petzke, F., Bordat, P., Herrmann, A., Reuther, E., Müllen, K., & Basché, T. (2002). Investigation of molecular dimers by ensemble and single molecule spectroscopy. Journal of Luminescence, 98, 23-33. CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. AbstractWe have investigated molecular dimers with different electronic coupling strengths by bulk and single molecule spectroscopy. In one of the dimers the two monomers (perylene-monoimide) are directly connected via a single bond while in the other one they are separated by the benzil motif. The close proximity of the monomers in the first case gives rise to excitonic band splitting which is clearly observable in the bulk absorption spectra. For the benzil structure the electronic interactions are governed by F .orster-type energy hopping between the monomers. Fluorescence intensity trajectories at the single molecule level show one-step and two-step bleaching behaviour which appears to be very similar for both dimers. However, emission spectra recorded simultaneously with the trajectories indicate spectral changes which allow to distinguish between weakly and strongly coupled dimers. In the latter case the spectral shape changes significantly when excitonic coupling has been lifted because of photochemical transformation of one of the monomers. r

Coherent Electronic Coupling versus Localization in Individual Molecular Dimers

“…The fluorescence yield f of the PM monomer, however, was reported [19] to be smaller than 1 ( f 0:95) and may be slightly different for the dimer and the monomer. Quenching of the monomer by the final bleaching product [11] seems to be highly unlikely because for PM in solution we find f 4:4 ns which is similar to the value found after the first chromophore bleached (Fig. 3).…”

“…For both molecules shown in Fig. 3 the fluorescence intensity has dropped to a lower level after a reversible dark state indicating that one of the chromophores has bleached [11]. Also, in both cases the fluorescence lifetime f has increased after the bleaching event, when emission occurs from a single chromophore.…”

“…[L S k rad dimer =k rad (monomer).] In this Letter we show by single molecule spectroscopy of individual molecular dimers [11][12][13][14] with a fairly large electronic coupling strength that the superradiance coherence sizes are widely distributed directly reflecting the interplay between intermolecular coupling and static disorder introduced by the polymer host. The chemical structure of the dimer allows for distinguishing localized and delocalized states by their particular emission spectra, too.…”

“…2 we present fluorescence spectra of two individual BPM dimers together with an ensemble fluorescence spectrum, which have been recorded in a homebuilt scanning confocal optical microscope [11]. A cw-Ar -ion laser operated at 488 nm was used for excitation, and the spectra were taken with an imaging spectrograph equipped with a liquid-nitrogen cooled charge coupled device camera.…”

Hidden Markov Model Analysis of Multichromophore Photobleaching

“…In some cases, aggregation of molecular systems is the focus of the experiment and the ability to quantify aggregation is of the utmost importance. [11][12][13] Fluorescence intermittency results from photophysical or photochemical transitions between emitting or "bright" states and nonemitting or "dark" states. Fluorescence intermittency is problematic because the photons deliver all the information about the system to the observer.…”