where l∞, l1 and k are empirical parameters that reflect the lmax values at n = ∞ and 1, respectively, and the rate of saturation. The data for our polyrotaxanes give l∞ = 503 nm, l1 = 172 nm, and k = 0.116. These values are similar to those deduced by Chalifoux and Tykwinski for their supertrityl polyynes (l∞ = 486 nm, l1 = 175 nm, and k = 0.116) .