0000000000181083
AUTHOR
Burkhard Fückel
Control of the electronic energy transfer pathway between two single fluorophores by dual pulse excitation.
We report on the control of the energy transfer pathway in individual donor-acceptor dyads by proper timing of light pulses matching the donor and acceptor transition frequencies, respectively. Excitation of both chromophores at virtually the same time induces efficient singlet-singlet annihilation, whereby excitation energy effectively flows from the acceptor to the donor. The dual pulse excitation scheme implemented here allows for all-optical switching of the fluorescence intensity at the single-molecule level. The population of higher excited states at the donor site was found to significantly increase the photobleaching probability.
Flexibility of phenylene oligomers revealed by single molecule spectroscopy
The rigidity of a p-phenylene oligomer (p-terphenyl) has been investigated by single molecule confocal fluorescence microscopy. Two different rylene diimide dyes attached to the terminal positions of the oligomer allowed for wavelength selective excitation of the two chromophores. In combination with polarization modulation the spatial orientation of the transition dipoles of both end groups could be determined independently. We have analyzed 597 single molecules in two different polymer hosts, polymethylmethacrylate and Zeonex. On average we find a 22 degrees deviation from the linear gas phase geometry (T = 0 K), indicating a rather high flexibility of the p-phenylene oligomer independent…
Probing the electronic state of a single coronene molecule by the emission from proximate fluorophores.
We measured electronic transitions of the 2D graphene-type molecule hexa-peri-hexabenzocoronene (HBC) at the single-molecule level. The large intersystem crossing rate and long triplet state lifetime in the range of seconds are prohibitive for direct single-molecule observation. By covalently coupling fluorescent acceptor molecules (perylenecarboximide, PMI) to HBC, efficient singlet energy transfer gives rise to strong PMI fluorescence. Confocal single-molecule fluorescence microscopy with two excitation colours matching the HBC and PMI transition frequencies, respectively, was conducted. Single HBC-6PMI molecules were readily observed via the PMI emission. It was found that after selectiv…
Quantification of the singlet-singlet annihilation times of individual bichromophoric molecules by photon coincidence measurements.
Singlet−singlet annihilation (SSA) times in individual bichromophoric molecules have been quantified by time-resolved photon coincidence measurements. An analytical expression has been derived to obtain the SSA times from the coincidence histograms. The results have been confirmed by Monte Carlo simulations. SSA was found to be about three times faster than the fluorescence lifetime of the chromophores. Considering the spectral overlap for SSA and for energy transfer from an excited to a ground state chromophore, we conclude that in the weak coupling limit for any arrangement of the two chromophores both processes occur on similar time scales.
Theoretical investigation of electronic excitation energy transfer in bichromophoric assemblies.
Electronic excitation energy transfer (EET) rates in rylene diimide dyads are calculated using second-order approximate coupled-cluster theory and time-dependent density functional theory. We investigate the dependence of the EET rates on the interchromophoric distance and the relative orientation and show that Forster theory works quantitatively only for donor-acceptor separations larger than roughly 5 nm. For smaller distances the EET rates are over- or underestimated by Forster theory depending on the respective orientation of the transition dipole moments of the chromophores. In addition to the direct transfer rates we consider bridge-mediated transfer originating from oligophenylene un…