Shizu and co-workers[171] used the same method (Equation 24) and found picosecond rate constants. For a series of ortho, meta, and para bridged tetracene dimers, rate constants of 2.02×10 11 s -1 , 1.36×10 8 s -1 , and 3.31×10 9 s -1 were reported. Two different para-configurations were examined (planar vs. free-rotated), and a difference of 3 orders of magnitude in the rate constant was observed, favouring the more flexible rotated configuration. Shizu and co-workers then juxtaposed a tetracene dimer allowed to equilibrate with both full quantum mechanical and split quantum mechanical molecular mechanical techniques; both techniques yielded geometries with very similar internal conversion speeds, with a quantum mechanical geometry rate of 8.74×10 11 s -1 , and a quantum mechanical molecular mechanical geometry rate of 5.05×10 11 s -1 . In all tetracene dimer cases, numerous small energy transition participating modes (∼50 cm -1 ) were observed, leading to the very fast rates of internal conversion.