X-ray radioluminescent crystalline colloidal arrays (CCAs) with highly tunable emission colors are synthesized using an emulsion polymerization procedure. An anthracene methyl methacrylate monomer is copolymerized within a poly(styrene-co-propargyl acrylate) basis to generate an x-ray radioluminescent CCA (87 nm). Due to the electrostatic repulsive forces between the colloidal nanoparticles, they are able to spontaneously self-assemble into an FCC structure. The CCAs possess a stop-band (i.e., rejection wavelength) in the visible regime that can be shifted across the visible spectrum by a change in the interplanar spacing, which is achieved by the addition or removal of deionized water. Typical anthracene radioluminescence spanning 400 – 515 nm with a maximum at 420 nm is detected when there is no rejection wavelength interference. However, a decrease in spontaneous emission at the rejection wavelength is observed when the rejection wavelength is shifted within the CCA’s radioluminescence. The radioluminescence decrease corresponding to the CCA’s rejection wavelength can be shifted across the entire radioluminescence of the CCA. In this way, the CCA’s radioluminescence can be manipulated by photonic means. Furthermore, the CCA’s color characteristics can be adjusted across the visible spectrum by x-ray induced sequential Förster Resonance Energy Transfer (FRET). This energy transfer is achieved by copolymerizing one or two additional organic fluorophores that form FRET pairs with anthracene and each other. A naphthalimide derivative that absorbs in the blue region where anthracene emits can be integrated within the x-ray radioluminescent CCA such that the CCA emits green, with a maximum at 535 nm, when pumped with an x-ray source. Additionally, a rhodamine B derivative that absorbs in the green region where naphthalimide emits can be copolymerized with the green-emitting CCA such that the CCA emits red, with a maximum at 630 nm, when pumped with an x-ray source. In this way, x-ray induced FRET or x-ray induced multiple sequential FRET is achieved, respectively, and the color of emitted light from the green- and red-emitting CCAs can be manipulated by photonic means to fine-tune the color characteristics of the liquid systems.

Fully organic, x-ray radioluminescent crystalline colloidal arrays: Spanning the visible spectrum via x-ray induced, sequential Förster resonance energy transfer (FRET)

ACS Fall 2021

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