Spin–lattice relaxation and hydrodynamical rotation of triphenylene

The viscosity and temperature dependence of 1 H, 2 H, and 13 C nmr relaxation rates of triphenylene were investigated. The observed η/T dependence of the reorientation correlation time, τ c , is compared with that derived from the work of Hu and Zwanzig based on hydro–dynamic rotation with 'stick' and 'slip' boundary conditions. In the hydrodynamic regime,τ = Cη/T. The observed slope, C experimental , is 6.2 ± 2 ns K/cP and the calculated values are C slip = 4.1 ± 0.6 ns K/cP and C stick = 31.0 ± 3.1 ns K/cP. These data imply that the reorientation of triphenylene obeys a near-slip condition. That is, rotation in the plane of the molecule encounters little resistance, but rotation of the plane of the molecule is resisted by shear forces in the solvent displaced during rotation. Expressions are given for Boltzmann-averaged free rotation times and comparisons are made with the η = 0 intercept and the times for slightly hindered rotation.