Remarkably large rotational diffusion rates have been determined for silica-attached 1-pyrene at the solid/air interface through time-dependent fluorescence anisotropy measurements. Diffusion rates D-parallel to and D-perpendicular to were determined to be 4 x 10(6) and 2 x 10(6) s(-1), respectively, by treating the motion of the attached moiety as an oblate ellipsoid of rotation. C-13 NMR measurements on solid, silica-attached benzene-1-C-13, acquired using conventional solution NMR methods, gave remarkable, high-resolution spectra. A lower limit for the rate of phenyl group motion was estimated to be 1.5 x 10(5) s(-1), consistent with the fluorescence anisotropy data measured for silica-attached 1-pyrene. Molecular mechanics models for phenyl attached to representative silanol surfaces predict rotational barriers for phenyl rotations in the 2-5 kcal/mol range.