Fig. 2

Goniophotometry and three-dimensional single-molecule orientation measurements. a–f Emission angle distributions of polymers with donor–acceptor ratios of ~8:1 and distances of ~1.5–2 nm were determined using calibrated power meters. b, e Isotropic acceptor emission (red, e) was observed after nearly perpendicular donor excitation in foils with random acceptor orientations. c, f When using samples with aligned acceptors instead, most of the light was emitted perpendicular (red, f) to the acceptor dipole moments, while nearly isotropic residual donor emission (green, c) demonstrates that the light-harvesting donors were still randomly orientated. Approximately 90% of the acceptor photons were re-directed into an angle range suitable for total reflection optical waveguiding with refractive indices of 1.5 or 1.9 (for details see Supplementary Figure 2, Supplementary Table 2, and Supplementary Note 2). The three acceptor distributions in f are obtained after (i) donor excitation and EET to aligned acceptors, (ii) direct excitation of aligned acceptors, and (iii) calculating an ideal cos²-distribution expected from perfectly aligned molecules. d When exciting randomly oriented dyes directly, as in conventional luminescent solar concentrators (cf. Fig. 1c), actually more light is emitted in unfavorable directions parallel to the excitation. Intensities at experimentally inaccessible detection angles were linearly extrapolated and values for angles >180° were mirrored from the values at 0°–180° (dotted lines in b–f). In b, c, e, and f, the scale denotes the angle with the transition dipole moment vector of aligned acceptors in stretched foils (Fig. 2a). In d, the scale denotes the angle with the excitation direction (inset in Fig. 2d). g–p Three-dimensional orientations of single acceptor molecules were determined by polarization modulated excitation with two different incident light directions (insets in g, h, l, m, Methods). i, k,n, p This yielded two different projections of the transition dipole moment orientation for individual molecules in samples with random (g, i and h, k) and aligned (l, n and m,p) acceptors, respectively. j,o From the two-dimensional projections i, k and n,p, the distribution of three-dimensional dipole orientations, j and o, for random and aligned acceptors are computed, respectively. These observations confirmed parallel alignment of the acceptor molecules in stretched foils in all three dimensions