Stimuli-induced adjustment of spatial distribution of fluorescence resonance energy transfer dyads in smart polymers

Smart polymers have received much attention due to their different responses to the induced stimuli. Polymers with fluorescent properties are also appealing for their potential applications in fluorescence chemosensors, optoelectronics, molecular thermometers, organic light-emitting diodes, molecular imaging, storage data security, drug delivery carriers, and encryption. Fluorescence resonance energy transfer (FRET) is an advanced optical mechanism on the basis of coupling fluorescent and photochromic materials as acceptors and donors. FRET phenomenon is highly considered due to its high sensitivity to spatial distance and ability of efficiency modulation. The spatial distance of dyads can be changed in response to the induced trigger in stimuli-responsive polymers. Therefore, stimuli-induced swelling, aggregation, or collapsing of smart polymers can be used to control the FRET dyad spatial distance and its efficiency. The FRET-based smart polymers include the advantages of both the FRET phenomenon and smart polymers through the critical role of FRET dyads, the spatial distance between them, and the overlap between their emission and absorbance spectra along with smart polymers' response. This review article highlights the application of FRET in smart polymers mainly for imaging and detection applications on the basis of FRET efficiency modulation with the smart polymer response toward various stimuli including temperature, pH, light, solvent, glucose, and mechanical force.