Chemical structure of the dyad containing three -phenylene groups as spacer (R: octyl). Absorption spectra of PDI, TDI, and the dyad (dotted line) in toluene. The spectral shift between the chromophore absorptions allows for selective excitation of PDI and TDI . The emission spectrum of PDI (dashed line) shows a strong overlap with the TDI absorption.
Confocal fluorescence microscopy setup with alternating excitation wavelengths and polarization modulation. APD: avalanche photo diode and BS: beam splitter (for details see text).
Typical fluorescence time trace of a single dyad embedded in PMMA. The sinusoidal intensity modulations originate from the rotating polarization of the excitation light. The slower rectangular intensity modulation stems from the alternating excitation wavelengths. A: and B: .
Scheme to visualize the meaning of the angles and . The angle between the transition dipoles (bold arrows) of both chromophores is denoted by . With our experimental setup only the projection on a 2D plane can be determined.
Histograms of the phase difference measured in PMMA and . The solid lines represent the best fits to the data (see text). The dashed lines are results from quantum chemical calculations (see Sec. IV). The means and have been calculated from the angle distributions in 3D space and in the 2D plane, respectively.
Comparison of the results of our fitting procedure (solid line, see also Fig. 5) to former experimental data obtained by a annular illumination method (Ref. 10). The dotted lines are results from our quantum chemical calculations (see Fig. 5 and text).
Relative ground-state energies of the twisted molecules calculated as described in the text [(엯) TZVPP and (●) SVP]. The solid line represents a fit of Eq. (1) to the SVP results, obtaining . The stick figure was calculated setting . In the inset the linear relation between the physical angle between the long axes of the chromophores and the angle between the transition dipoles is plotted.
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