From static to active photoluminescence tuning: functional spacer materials for plasmon–fluorophore interaction

Abstract

Plasmon-triggered modulation of fluorophores’ photoluminescence has introduced tremendous opportunities for diverse applications, such as: sensing, biolabeling, novel light sources, integrated optical communication, and data-processing. Thus, numerous plasmonic–fluorophore hybrid systems have been designed and studied providing deep insight into nanoscale light-matter interactions as well as the ability to control spontaneous photoluminescence of the fluorophores. In such systems, the distance between plasmonic components and fluorophores plays a crucial role in plasmon-exciton coupling and the overall optical characteristics of the fluorophores. So far, various dielectric materials, such as organic and inorganic thin films and biomolecular linkers have been exploited as the spacer layer in these systems. Once they have been fabricated, most hybrid systems are based on static spacers, and thus, do not enable active changes of the optical properties. Consequently, there is a growing demand to develop novel hybrid systems in which the optical properties can be actively tuned via variation of parameters to broaden the applications of such devices. Therefore, incorporation of responsive materials like liquid crystals and stimuli-responsive polymers, as a separating layer, can ensure the active tuning of the fluorophores’ optical properties in such hybrid systems. Suitable choices of material, as the spacer layer, make it possible to take advantage of both the individual properties of the separating layer and the modulation of plasmon-exciton coupling for the desired purpose. In this review, various materials that have been applied as the spacer layer in view of their advantages and disadvantages are highlighted. Moreover, the preparative techniques of these spacer layers will be discussed with emphasize on the flourishing field of active photoluminescence tuning, where stimuli-responsive polymers can be believed to be promising spacer candidates in plasmonic–fluorophore hybrid systems.