  We present an analytic theory for the optical properties of ellipsoidal
plasmonic particles covered by anisotropic molecular layers. The theory is
applied to the case of a prolate spheroid covered by chromophores oriented
parallel and perpendicular to the metal surface. For the case that the
molecular layer resonance frequency is close to being degenerate with one of
the particle plasmon resonances strong hybridization between the two resonances
occur. Approximate analytic expressions for the hybridized resonance
frequencies, their extinction cross section peak heights and widths are
derived. The strength of the molecular - plasmon interaction is found to be
strongly dependent on molecular orientation and suggest that this sensitivity
could be the basis for novel nanoparticle based bio/chemo-sensing applications.
