The rotational relaxation of perylene and tetracene in hexadecane has been studied at several temperatures by femtosecond fluorescence upconversion. The initial emission anisotropy values of both D-2h symmetric fluorophores are now found to be very close to the theoretical value of 0.4, and the anisotropy decay observed with subpicosecond time resolution can no longer be described as a biexponential. The traditional in-plane and out-of-plane rotational diffusion time constants of perylene in hexadecane are verified to be linearly dependent on viscosity/temperature. Moreover, a third, ultrafast rotation, empirically fit to a time constant of similar to450 fs for perylene and similar to600 fs for tetracene, has been found. It is independent of temperature and viscosity, and the amplitude ("beta(fast)") explains the previously described "r(0) defect". Since beta(fast) is similar to0.03 for tetracene vs similar to0.05 for perylene, we presently suggest that "in-plane" femtosecond libration of the molecules within a solvent pocket yields the observed anisotropy.