, where η is the viscosity. For toluene the diffusion rate is 1.2×10 10 M -1 s -1 , and for chloroform it is 1.3×10 10 M -1 s -1 . This difference (10%) is smaller than the difference in SF rate constants of TIPS-Pn in the two solvents, but the Stokes-Einstein relation is a simplified representation of diffusion, and the trend is consistent. We note the two solvents also have different dielectric constants (2.38 for toluene compared to 4.81 for chloroform). It has been suggested that charge-transfer states may play a role in SF, which would be influenced by the dielectric constant, and may also be a contributing factor to SF. We also note that Dvořák et al. confirmed that there was negligible aggregate formation below 28 mM for solutions of TIPS-Pn in chloroform. Given the solubility of TIPS-Pn in toluene is similar to chloroform, we expect that aggregation was absent in the solutions studied here.