In this study, surface plasmon resonance studies of Langmuir - Blodgett multilayers have been used to characterize an optically highly absorbing zwitterionic material which would be difficult to otherwise analyse. By fitting reflectivity data with Fresnel theory for a range of wavelengths it has been possible to obtain the real and imaginary parts of the assumed-isotropic dielectric optical permittivity over the visible part of the spectrum. These results show an asymmetric resonance peak which may be interpreted as being a composite of two resonances, one associated with an intermolecular dipole transition and one with an intramolecular dipole.