Static orientational factor for two-dimensional system with moments randomly distributed on cone with * = 58.4°.~15% in the deconvolutions. Moreover, the percent discrepancies are nearly constant, and the linearity of a plot similar to that in Figure 5 is hardly affected. Hence, our conclusion that the two-dimensional two-particle theory for (?(r) works well for all of the densities shown in Figure 5 is not sensitive to the model assumed for the orientational distribution of transition moments.Polarized fluorescence profiles obtained at higher chromophore densities than those shown in Table I show an interesting anomaly in that the fluorescence components /E, I_ do not converge together at long times. At 1511 X 10"6 chromophores/Á2, the two profiles intersect after ~1 ns, and I± decays more slowly than It at long times. At 2932 X 10"6 chromophores/Á2,1± remains below /E at all times, and the phenomenological decay times are markedly reduced. These ODRB densities are extremely large (the latter density corresponds to packing and average of ~16 chromophores per circle of radius R0 = 44.7 Á), and these polarization effects may result from excimer formation.We showed earlier8 that the three-dimensional two-particle theory of Huber et al.1 furnishes an accurate description of transport in solution for reduced concentrations up to ~3 in the absence of orientational correlation. Figure 5 indicates that the two-dimensional analogue (eq 3) of the Huber theory is valid for reduced ODRB densities CD up to ~5. This result is of particular interest, because density expansions of (?(Z) converge more slowly in systems of lower dimensionality. Hence, one may expect the demonstrated validity of the two-particle theory to be exhibited a fortieri in random three-dimensional systems; the system dimensionality does not pose fundamental problems in our understanding of singlet excitation transport.

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We have obtained evidence for a transient cyclic Nf anion from isotopic labeling studies. Calculations suggest that the transient