Absorption (black lines) and emission ensemble spectra (gray lines) of (a) PDI and TDI, (b) dyad 1 and (c) dyad 2. Each compound has been dissolved in toluene.
Emission spectra of single dyads 1 and 2 embedded in PMMA at . In 2 intramolecular energy transfer is slow enough such that weak emission from the donor is observed .
Fluorescence time trace of the same single dyad 2 at , the emission spectrum of which is shown in Fig. 2. After PDI bleached first, seen in the drop of the intensity. The corresponding rise∕decay time profiles before and after bleaching are shown in the inset. The profiles consist of before and counts after bleaching of PDI. The difference shown in the upper part of the inset originates from the energy transfer (Ref. 31).
Distribution of single molecule EET rates of dyad 2, obtained at room temperature. The open bars represent the rates determined from the rise∕decay time profiles, while the filled bars are calculated according to Förster theory from spectral overlaps, each on a single molecule level. The solid lines show a simulated rate distribution originating solely from different molecular conformations. This distribution has been scaled to fit both histograms. For more details see text.
Inhomogeneous distributions of electronic transition frequencies from dyads 1 and 2, for both donor (PDI) and acceptor (TDI). At the distributions of purely electronic zero-phonon lines are plotted [(a) and (b)] while at room temperature (c) the distributions of emission maxima are shown. The bold lines are Gaussians fitted to the inhomogeneous distributions.
Emission spectra of single dyads 1 (a) and 2 (b) embedded in PMMA at low temperature (, ). In 1 energy transfer is so fast that no donor emission is visible.
Emission spectra from a single dyad 2, taken at . Spectral shifts which are stronger for PDI lead to variations in the ratio , which nicely correlates to the estimated spectral overlaps, .
Distribution of single molecule EET rates of dyad 1 obtained at . The open bars represent the rates determined from donor (PDI) excitation spectra, while the filled bars are calculated from the spectral overlaps according to Förster theory. The solid lines show a simulated rate distribution solely originating from different molecular conformations. This distribution has been scaled to fit both histograms.
Experimentally determined energy transfer rates plotted vs the calculated spectral overlaps, see text. (Dyad , dyad 2: room temperature). The solid lines have been calculated according to Förster theory [Eq. (1)]. The dashed lines represent linear fits to the data.
Spectral overlap between single molecule emission (PDI) and absorption (TDI) spectra at (sharp lines) and at room temperature. For better visibility the intensities of the room temperature spectra are enlarged five times. For more details see text.
Comparison of transfer rate distributions at room temperature (RT) and (low temperature, LT) calculated within Förster theory. The calculation is based on the experimentally observed inhomogeneous distributions of dyad 1 at [Fig. 5(a)].
Chemical structures of the donor∕acceptor dyads 1 and 2.
Summary of EET and molecular parameters for dyads 1 and 2.
Parameters of the fitted distributions as plotted in Fig. 5.
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