Light-emitting supramolecular coordination complexes (SCCs) have been widely studied for applications in the chemical and biological sciences. Herein, we report the coordination-driven self-assembly of two highly emissive platinum(II) supramolecular triangles (1 and 2) containing BODIPY-based bridging ligands. The metallacycles exhibit favorable anticancer activities against HeLa cells (IC of 6.41 and 2.11 μM). The characteristic ∼570 nm fluorescence of the boron dipyrromethene (BODIPY) moieties in the metallacycles permits their intracellular visualization using confocal microscopy. Additionally, the BODIPY fluorophore is an excellent photodynamic agent, making the metallacycles as ideal therapeutics for photodynamic therapy (PDT) and chemotherapy. In vitro studies demonstrate that the combination indexes against HeLa cells are 0.56 and 0.48 for 1 and 2, respectively, confirming their synergistic anticancer effect. More importantly, these SCCs also exhibit superior anticancer efficacy toward cisplatin-resistant A2780cis cell line by combining PDT and chemotherapy, showing promise in overcoming drug resistance. This study exploits a multicomponent approach to self-assembled metallacages that enables design of effective theranostic agents wherein the platinum acceptors are toxic chemotherapeutics and the BODIPY donors are imaging probes and photosensitizers. Since each piece may be independently tuned, i.e., Pt(II) polypyridyl fragment swapped for Pt(II) phosphine, the activity may be optimized without a total redesign of the system.
Achieving directional charge transfer across semiconductor interfaces requires careful consideration of relative band alignments. Here, we demonstrate a promising tunable platform for light harvesting and excited-state charge transfer based on interfacing β-Pb x V 2 O 5 nanowires with CdSe quantum dots. Two distinct routes are developed for assembling the heterostructures: linker-assisted assembly mediated by a bifunctional ligand and successive ionic layer adsorption and reaction (SILAR). In the former case, the thiol end of a molecular linker is found to bind to the quantum dot surfaces, whereas a protonated amine moiety interacts electrostatically with the negatively charged nanowire surfaces. In the alternative SILAR route, the surface coverage of CdSe nanostructures on the β-Pb x V 2 O 5 nanowires is tuned by varying the number of successive precipitation cycles. High-energy valence band X-ray photoelectron spectroscopy measurements indicate that "mid-gap" states of the β-Pb x V 2 O 5 nanowires derived from the stereoactive lone pairs on the intercalated lead cations are closely overlapped in energy with the valence band edges of CdSe quantum dots that are primarily Se 4p in origin. Both the midgap states and the valence-band levels are in principle tunable by variation of cation stoichiometry and particle size, respectively, providing a means to modulate the thermodynamic driving force for charge transfer. Steady-state and time-resolved photoluminescence measurements reveal dynamic quenching of the trapstate emission of CdSe quantum dots upon exposure to β-Pb x V 2 O 5 nanowires. This result is consistent with a mechanism involving the transfer of photogenerated holes from CdSe quantum dots to the midgap states of β-Pb x V 2 O 5 nanowires. ■ INTRODUCTIONTuning interfaces between disparate semiconductors, between molecules and semiconductor surfaces, and between semiconductors and metals remains of paramount importance for electronics, optoelectronics, photocatalysis, photovoltaics, and electrochemical energy storage. 1−4 Interfaces assume special significance for nanostructures given their high surface-tovolume ratios. Nanoscale heterostructures are of particular interest for photocatalysis owing to the tunability of the energies of the valence and conduction band edges of semiconductors as a function of finite size and doping, which allows for different components performing discrete functions to be assembled within modular platforms to facilitate sequential light-harvesting, charge transfer, and catalytic processes. 4,5 To enable programmable cascades of directional charge transfer reactions, heterostructures need to be designed keeping in mind several considerations such as the nature of the interface, the thermodynamics of band alignments between different components, and the kinetics of charge transfer. In this work, we have sought to design nanoscale heterostructures to exploit the availability of midgap states energetically positioned between the valence and conduction bands of a transition metal oxi...
We report a suite of coordination-driven self-assembled prisms for heterogeneous electrocatalytic oxygen reduction (ORR) differing in the molecular clips linking two porphyrin faces in a cofacial arrangement. ORR activities and selectivities of monomeric CoTPyP along with cofacial prisms Ox-Co, Oxa-Co, and Benzo-Co were probed using cyclic voltammetry and rotating ring-disk techniques. All species were immobilized as heterogeneous catalysts on glassy carbon electrodes using a Nafion ink method. The selectivities of Ox-Co, Oxa-Co, and Benzo-Co prisms towards H O as determined by RRDE were 87, 97, and 75 %, respectively. The current density of the Oxa-Co plateaus at five times that of Pt/C when normalized per Co/Pt. The high synthetic yield (79 %), competitive overpotential (η ≈800 mV) and high selectivity (%H O ≈97 %) of the Oxa-Co highlights how self-assembly can be used to address multi-electron multi-proton transformations using polynuclear catalysts.
A reversible Fe /Fe redox couple of an azamacrocyclic complex is evaluated as an electrolyte with a pH-tunable potential range for aqueous redox-flow batteries (RFBs). The Fe complex is formed by 1,4,7-triazacyclononane (TACN) appended with three 2-methyl-imidazole donors, denoted as Fe(Tim). This complex exhibits pH-sensitive redox couples that span E (Fe /Fe )=317 to -270 mV vs. NHE at pH 3.3 and pH 12.8, respectively. The 590 mV shift in potential and kinetic inertness are driven by ionization of the imidazoles at various pH values. The Fe /Fe redox is proton-coupled at alkaline conditions, and bulk electrolysis is non-destructive. The electrolyte demonstrates high charge/discharge capacities at both acidic and alkaline conditions throughout 100 cycles. Given its tunable redox, fast electrochemical kinetics, exceptional stability/cyclability, this complex is promising for the design of aqueous RFB catholytes and anolytes that utilize the earth-abundant element iron.
We assembled eight cofacial porphyrin prisms using MTPyP (M = Co(II) or Zn(II), TPyP = 4-tetrapyridylporphyrin) and functionalized ruthenium-based “molecular clips” using coordination-driven self-assembly. Our approach allows for the rapid synthesis of these architectures in isolated yields as high as 98% for the assembly step. Structural and reactivity studies provided a deeper understanding of the role of the building blocks on the oxygen reduction reaction (ORR). Catalytic efficacy was probed by using cyclic and hydrodynamic voltammetry on heterogeneous catalyst inks in aqueous media. The reported prisms showed outstanding selectivity (>98%) for the kinetically hindered 4e–/4H+ reduction of O2 to H2O over the kinetically more accessible 2e–/2H+ reduction to H2O2. Furthermore, we have demonstrated significant cofacial enhancement in the observed catalytic rate constant k s (∼5 orders of magnitude) over the mononuclear analogue. We conclude that the steric bulk of the clip plays an important role in the structural dynamics of these prisms, which in turn modulates the ORR reactivity with respect to selectivity and kinetics.
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