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The ability to prepare and tailor synthetic analogues of native bacteriochlorophylls enables diverse applications. A de novo route entails dimerization of a dihydrodipyrrin-acetal to afford the corresponding 5-methoxy and/or 5-unsubstituted bacteriochlorin, wherein each pyrroline ring contains a gem-dimethyl group to ensure stability toward adventitious dehydrogenation. The presence of a 5-methoxy group facilitates bromination at the distal meso-(15-)position. While bromination of 5-unsubstituted bacteriochlorins typically affords a mixture of brominated products, here the presence of two substitution patterns (2,12-dicarboethoxy, 2,12-diacetyl) has been found to facilitate selective meso-bromination in the absence of the methoxy substituent. The introduction of a single meso-bromine atom in a bacteriochlorin opens opportunities for Pd-mediated derivatization, which include (1) preparation of four ethynylphenyl building blocks (and two benchmark bacteriochlorins) with long-wavelength absorption bands tuned across 725–757 nm, for use in preparation of multichromophore arrays; (2) installation of a bioconjugatable group to free base bacteriochlorins or a copper bacteriochlorin, the latter for possible use in photoacoustic imaging; and (3) installation of an S-acetylthio group for surface attachment. Altogether, 25 new bacteriochlorins are described including 5 meso-bromobacteriochlorin intermediates and 12 target bacteriochlorins. [ABSTRACT FROM AUTHOR]

Solubilization of hydrophobic tetrapyrrole macrocycles and other fluorophores in aqueous solution has been achieved by covalent attachment to the terminus of an amphiphilic polymer, thereby affording a single-fluorophore–single-chain nanoparticle (SCNP). The polymer is a heterotelechelic random polyacrylate/polyacrylamide copolymer bearing hydrophobic and hydrophilic pendant groups. The polymer has a folded unimeric morphology (∼13 nm hydrodynamic diameter) in 1 M NaCl aqueous solution as indicated by dynamic light-scattering spectroscopy. Five hydrophobic organic fluorophores (coumarin, perylene, two chlorins, one phthalocyanine) have been synthesized with a conjugatable tether. Covalent conjugation of the fluorophore–maleimide to the polymer terminus via thiol–maleimide reaction was carried out in DMF. The resulting fluorophore–SCNP in 1 M NaCl aqueous solution exhibited spectral features and fluorescence quantum yield comparable to those of the respective hydrophobic benchmark in toluene. This single-fluorophore–single-polymer strategy bypasses the challenging and often idiosyncratic syntheses of water-soluble tetrapyrrole macrocycles by using the polymer as a general aqueous solubilization package, and in so doing opens up opportunities for the application of hydrophobic fluorophores in the life sciences. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) is essential for water splitting to produce H2 gas, and its kinetically sluggish nature involving the transfer of four electrons hinders the energy-conversion efficiency and increases the cost; therefore, there is an urgent need to explore OER electrocatalysts with high efficiency and durability. The abundant internal cavities in hollow particles can provide a larger number of active sites and promote the electron/mass transport in the OER, and thus are highly desirable. However, their large-scale facile preparation, especially for small-sized particles, remains challenging. We present herein a scalable high-frequency ultrasonic pyrolysis strategy to prepare ultrafine Fe-doped NiO porous hollow spheres as OER catalysts. In this aerosol droplet-mediated method, a 3 MHz high-frequency ultrasonic wave ensures the formation of small sized droplets and oxide hollow products. The prepared Ni0.9Fe0.1O hollow spheres with a NiO phase exhibit a uniform and small size of ∼200 nm and a wall thickness of ∼10 nm, and they are highly porous with a specific surface area of about 50 m2 g−1. The fine and hollow structure increases the OER active site number, while the synergistic effect of Fe and Ni elements optimizes the intrinsic activity. As a result, the Ni0.9Fe0.1O hollow spheres have a low OER overpotential for achieving a current density of 10 mA cm−2 (288 mV), suggesting an excellent OER performance. During potentiostatic testing, almost no decrease in the current density occurred upon catalyzing for 18 h, indicating the high stability of our catalyst, which may be because the well-crystallized NiO phase may suppress the rapid dissolution of the doped Fe in catalyzing the OER, thereby diminishing an appreciable activity loss. This synthesis strategy can be applied to other ultrafine hollow particles. [ABSTRACT FROM AUTHOR]

Synthetic bacteriochlorins, analogues of native bacteriochlorophylls, provide absorption in the near-infrared spectral region and hence are valuable for fundamental studies in photochemistry and applications ranging from solar energy conversion to photomedicine. The full realization of such opportunities hinges on access to synthetically malleable bacteriochlorins. Here, two established routes that rely on self-condensation of a dihydrodipyrrin-acetal or dihydrodipyrrin-carboxaldehyde have been exploited to prepare 6 bacteriochlorins (2 new, 4 known in improved fashion). Each bacteriochlorin contains a gem-dimethyl group in the reduced, pyrroline ring to ensure stability toward adventitious dehydrogenation. These and related synthetic bacteriochlorins have been derivatized to tailor the perimeter of the macrocycle with diverse groups, affording 9 additional new bacteriochlorins and 4 known bacteriochlorins. By direct installation and/or derivatization, the scope of attached entities in this collection includes alkyl, amino, aryl, bromo, carboethoxy, oxo, phenylethynyl, and pyridyl. The bacteriochlorins are suited for surface attachment, bioconjugation, water-solubilization, vibrational studies, and elaboration into multichromophore arrays. Altogether the synthesis of 25 new compounds (11 bacteriochlorins, 14 precursors) is described. [ABSTRACT FROM AUTHOR]