Here, we present an overview of the ellipsometric characterization of hybrid thin films and metal nanoparticles by surface plasmon resonance (SPR) spectroscopy, together with the dynamic control of the optical properties of the latter for applications in optoelectronic devices. A description of traditional techniques used for the determination of the thickness and refractive index of organic thin films deposited over the SPR planar sensing platforms is presented, with a discussion of the most recent applications in the ellipsometric characterization of thin film of metal nanoparticles and graphene layers. We conclude by describing recent results developing a dynamically tunable plasmonic pixel, where the electric-field-controlled alignment of gold nanorods in a colloidal suspension can enable optical switching at frequencies greater than megahertz.