CONFINING AN ORGANIC MOLECULE IN A NANOCAVITY: EFFECT ON ROTATIONAL/VIBRATIONAL MOTION AND ITS CONSEQUENCE FOR SPIN DEPHASING.

Recently, it was found that the strongly temperature-dependent spin dephasing time of bound electrons in the organic molecule tris(8-hydroxyquinoline aluminum), or Alq3, increases when a few of these molecules are confined within 1-2 nm sized nanocavities in porous alumina. What causes this increase is not well understood, but one possibility is that the rotational/vibrational modes of the molecule are altered inside a nanocavity, leading to suppression of spin coupling with these modes and a concomitant increase in the spin dephasing time. To test this possibility, we have carried out mid-infrared spectroscopy of few molecule clusters confined within 1-2 nm sized nanocavities. Their spectrum is considerably different from that of bulk powders of molecules, indicating that at least some vibrational modes (in the mid infrared range) have been altered. This may be a possible cause for weakening of spin-environment coupling inside a nanocavity, resulting in an increase in the spin dephasing time