Figure 4.

a) A representation of the terms from equation 4; ω_SP represents the energy difference between states, k_1P→1S is the rate of relaxation, g_SS and g_PP are the lineshape functions which represent the fluctuations of each state, and g_SP describes degree to which those fluctuations are shared (or correlated). b) Two extreme cases, where the fluctuations are completely uncorrelated (leading to dephasing on a 10 fs time scale, or completely correlated, leading to dephasing only from population relaxation. c) Data from point D from figure 3, which shows two frequencies, for which we fit the model described in supporting information, given known lineshape parameters. The fit shows a high degree of correlation (C=0.97 or C=0.98 for the two observed modes, respectively) is needed to reproduce the observed excitonic lifetimes.