Metal–organic frameworks (MOFs) can provide a matrix for the assembly of organic chromophores into well-defined geometries, allowing for tuning of the material properties and study of structure–property relationships. Here, we report on the effect of the coordinated metal ion on the luminescence properties of eight isostructural MOFs having the formula M¹ ₂M²L₃(DMF)₂ (M¹ = M² = Zn (1), Cd (2), Mn (3), Co (4); M¹ = Zn, M² = Cd (5), Mn (6), Co (7); M¹ = Co, M² = Mn (8); L = trans-4,4′-stilbene dicarboxylate), synthesized by reaction of the appropriate metal nitrate or mixtures of metal nitrates with LH₂ in DMF. The crystal structures of 2, 3 and 5–8 were determined by X-ray diffraction to be composed of trinuclear metal clusters linked by stilbene dicarboxylate linkers in a paddlewheel geometry, extending to form a 2-D layered structure. In the mixed-metal cases, the larger metal ion was found to occupy the octahedral site in the cluster while the smaller ion occupies the tetrahedral positions, suggesting a selective, ligand-directed assembly process for the mixed-metal species. Variable temperature magnetic measurements for paramagnetic MOFs 3 and 6–8 were consistent with the site occupancies determined crystallographically, and indicated weak intra-cluster antiferromagnetic coupling for 3 and 8. Comparison between the crystal structures of 2, 3 and 5–8 and those reported for 1 and 4 in the literature reveal close resemblances between linker environments, with important intermolecular stilbene–stilbene geometries that are comparable in all cases. Interestingly, pale-colored 1–3 and 5–7 display very similar emission profiles upon excitation at λ_ex = 350 nm, whereas dark-colored 4 and 8 do not exhibit detectable emission spectra. The bright, well-resolved luminescence of 1, 2 and 5 is ascribed to rigidification of the linker upon coordination to the d¹⁰ metal ions, whereas the weaker emission observed for 3, 6 and 7 is presumably a result of quenching due to close proximity of the linker to one or more paramagnetic ions. Time-resolved measurements for 1, 2, 5 and 6 reveal biexponential emission decays, where the lifetime of the longer-lived state corresponds to observed variations in the nearest-neighbor cofacial stilbene–stilbene distances in their crystal structures. For 3, a monoexponential decay with shorter lifetime was determined, indicating significant paramagnetic quenching of its emissive state.

Estuaries can behave as plastic pollution hotspots, although the dynamics of accumulation in these unique habitats are not understood. We quantified the current levels of meso-, micro-, and nanoplastic pollution in four Los Angeles County estuaries for the first time, as a function of distance from the water outlet and local population density. Fourier-transform infrared spectroscopy (FTIR) and microscope imaging revealed the presence of six types of plastic; polyethylene or polypropylene dominated the meso- and microplastic, and nanoplastics were identified as mainly polyolefin fibers. The distribution was heterogeneous throughout, although the sand between the river mouth and ocean generally contained more plastic than inland control samples. Population density did not appear to affect the abundance of plastic estuarine pollution. Other factors, such as waste treatment effluent, recreation, and river geography, may contribute to plastic deposition. A positive correlation between meso- and microplastic abundance provides insight into such mechanisms for accumulation.

Branched poly(ethylene-imine) can be tagged with luminescent dyes (e.g., fluorescein isothiocyanate and tetramethylrhodamine isothiocyanate) and used to precipitate spherical silica particles from 10s-to-100s of nm diameter size under mild conditions. These dye–PEI/SiO₂ nanoparticles are highly compatible with polar solvents to give bright fluorescent suspensions, and detailed photophysical characterization reveals well-separated dye moieties with an approximately homogeneous dispersion of dye–PEI conjugate throughout the SiO₂ matrix. Reaction of PEI amine groups incorporated at the particle surface affords a simple method for post-synthesis functionalization of these materials, and the formation of FITC/Eosin-Y fluorescence resonance energy transfer pair-tagged particles and SiO₂@Au core–shell nanocomposites using this strategy is demonstrated. This bio-inspired approach to multi-functional SiO₂ nanoparticles provides a range of potential advantages over traditional “inorganic” syntheses of similar materials, as it proceeds through a scalable, single-step reaction using inexpensive reagents, enables efficient incorporation of luminescent species into the resulting particles with very limited dye aggregation, and provides nanoparticles that do not require post-synthesis modification for further conjugation with species of interest. The method offers a simple means to generate complex nanocomposites, whereby a host of desired species can be incorporated both inside and on the surface of biocompatible SiO₂ nanoparticles.