Photoluminescence (PL) spectra were measured for dodecene-capped Si nanocrystals with a wide range of average diameters, from 1.8 to 9.1 nm. Nanocrystals larger than 3 nm exhibited relatively high PL quantum yields of 30%−45%. Smaller nanocrystals exhibited lower quantum yields that decreased significantly with reduced size. Because smaller nanocrystals also have lower optical absorption there is a significant biasing of the PL spectra by the larger nanocrystals. We show that with proper accounting of polydispersity and sizedependent quantum yields and optical absorption the effective mass approximation (EMA) accurately estimates the average diameter of silicon (Si) nanocrystals from experimentally determined PL emission peak energies. A finite confinement model is presented that explains the decreased PL quantum yields of the smaller diameter nanocrystals.

Metabolic engineering has facilitated the production of pharmaceuticals, fuels, and soft materials but is generally limited to optimizing well-defined metabolic pathways. We hypothesized that the reaction space available to metabolic engineering could be expanded by coupling extracellular electron transfer to the performance of an exogenous redox-active metal catalyst. Here we demonstrate that the electroactive bacterium can control the activity of a copper catalyst in atom-transfer radical polymerization (ATRP) via extracellular electron transfer. Using, we achieved precise control over the molecular weight and polydispersity of a bioorthogonal polymer while similar organisms, such as , showed no significant activity. We found that catalyst performance was a strong function of bacterial metabolism and specific electron transport proteins, both of which offer potential biological targets for future applications. Overall, our results suggest that manipulating extracellular electron transport pathways may be a general strategy for incorporating organometallic catalysis into the repertoire of metabolically controlled transformations.

The supramolecular packing mode of organic π-conjugated molecules in the solid state plays a crucial role in determination of the resulting material properties and functionalities. Control and understanding of supramolecular packing of individual building blocks constitute an important step toward optoelectronic and biomedicine. In this work, we have designed and synthesized a series of bis(pyrene) derivatives, i.e., BP1−BP4 with 1,3-dicarbonyl, pyridine-2,6dicarbonyl, oxaloyl and benzene-1,4-dicarbonyl as linkers, respectively. In solution, all compounds showed low fluorescence quantum yields (Φ < 1.7%) in variable organic solvents due to the twisted intramolecular charge transfer (TICT). In a sharp contrast, BP1 and BP2 in the solid state were selfassembled to form J-type aggregates with almost 30-fold fluorescence enhancement (Φ was up to 32.6%) compared to that in solution. Nevertheless, H-type aggregates of BP3 and BP4 were observed with poor emissive efficiencies (Φ < 3.1%). The proposed molecular aggregates types were confirmed by powder X-ray patterns and single crystal structures. The slipping angles of adjacent molecules of J-type aggregates were 41.07−44.58°, which were smaller than that (64.58−68.45°) in H-type aggregates. Subsequently, B3LYP/6-31G quantum chemistry calculation was performed and the results indicated that the excimeric emission of BP1−BP4 aggregates was closely related to their molecular packing orientation and parameters. Furthermore, the morphologies of supramolecular aggregates based on BP1−BP4 were observed by transmission electron microscope (TEM) and the results showed that BP1 and BP2 were dot-shape nanoaggregates with 2−6 nm in diameters, while BP3 and BP4 showed sheet-like morphologies with 5−10 nm in width and 20−100 nm in length. The nanoaggregates of BP1 and BP2 coated with F108 surfactants showed good pH and photostability in physiological condition. Finally, the nanoaggregates of BP1 and BP2 were successfully employed as fluorescence nanoprobes for lysosome-targeted imaging in living cells with negligible cytotoxicity.

Performing radical polymerizations under ambient conditions is a significant challenge because molecular oxygen is an effective radical quencher. Here we show that the facultative electrogen Shewanella oneidensis can control metal-catalyzed living radical polymerizations under apparent aerobic conditions by first consuming dissolved oxygen via aerobic respiration, then directing extracellular electron flux to a metal catalyst. In both open and closed containers, S. oneidensis enabled living radical polymerizations without requiring the pre-removal of oxygen. Polymerization activity was closely tied to S. oneidensis anaerobic metabolism through specific extracellular electron transfer (EET) proteins and was effective for a variety of monomers using low (ppm) concentrations of metal catalysts. Finally, polymerizations survived repeated challenges of oxygen exposure and could be initiated using lyophilized or spent (recycled) cells. Overall, our results demonstrate how the unique ability of S. oneidensis to use both oxygen and metals as respiratory electron acceptors can be leveraged to address salient challenges in polymer synthesis.

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