Preparation, self-assembly of SiO₂/PNIPAm complex microgels and their manipulation of fluorescence emission for organic dyes

In this study, a novel strategy for manipulating fluorescence emission of organic dyes is reported, which is based on coupling optical properties of colloidal crystals (CCs) with responsive microgels. Firstly, SiO₂ microspheres doped with three kinds of organic dyes (Rhodamine B, RhB; fluorescein isothiocyanate, FITC; commercial cationic Fluorescent Yellow, X-10GFF) were prepared and they were used as the cores to synthesize SiO₂/PNIPAm complex microgels doped with organic dyes by free radical polymerization. Then 3D self-assembled CCs of the complex microgels were fabricated by centrifugation. The microstructure of the complex microgel was characterized by Fourier transform infrared (FTIR), transmission electron microscopy (TEM), thermogravimetric (TG), dynamic light scattering (DLS), and differential scanning calorimeter (DSC). Moreover, the effect of doping organic dyes and temperature on self-assembly of the microgels were investigated. Manipulation of fluorescence emission for organic dyes by CCs was studied by photoluminescence (PL) and UV-visible spectrophotometer (UV-Vis). The results indicate that, due to the soft and thermosensitive property of PNIPAm shell, continuous adjustment to the photonic bandgap (PBG) of the CCs can be achieved conveniently by varying concentrations of the complex microgels or ambient temperatures, and when PBG of the CCs overlaps with the fluorescence emission peak of the organic dye, fluorescence emission of the organic dye can be manipulated.