Showing papers by "Cheng Wang published in 2015"

Photosensitizing Metal–Organic Framework Enabling Visible-Light-Driven Proton Reduction by a Wells–Dawson-Type Polyoxometalate

Abstract: A simple and effective charge-assisted self-assembly process was developed to encapsulate a noble-metal-free polyoxometalate (POM) inside a porous and phosphorescent metal–organic framework (MOF) built from [Ru(bpy)3]2+-derived dicarboxylate ligands and Zr6(μ3-O)4(μ3-OH)4 secondary building units. Hierarchical organization of photosensitizing and catalytic proton reduction components in such a POM@MOF assembly enables fast multielectron injection from the photoactive framework to the encapsulated redox-active POMs upon photoexcitation, leading to efficient visible-light-driven hydrogen production. Such a modular and tunable synthetic strategy should be applicable to the design of other multifunctional MOF materials with potential in many applications.

Highly Active Hydrogen Evolution Electrodes via Co-Deposition of Platinum and Polyoxometalates.

Abstract: A highly active hydrogen evolution reaction (HER) electrode with low Pt loading on glassy carbon (GC) has been prepared by anodic platinum dissolution and co-deposition of polyoxometalates. TEM, EDS, XPS, CV, and ICP-MS analyses gave a Pt loading of 50–100 ng/cm2, corresponding to a Pt coverage of only 0.08–0.16 monolayer. With an overpotential of 65 mV at 20 mA/cm2, the modified GC has a HER activity comparable to that of the commercial Pt working electrode.

Towards quantification of vibronic coupling in photosynthetic antenna complexes.

Abstract: Photosynthetic antenna complexes harvest sunlight and efficiently transport energy to the reaction center where charge separation powers biochemical energy storage. The discovery of existence of long lived quantum coherence during energy transfer has sparked the discussion on the role of quantum coherence on the energy transfer efficiency. Early works assigned observed coherences to electronic states, and theoretical studies showed that electronic coherences could affect energy transfer efficiency—by either enhancing or suppressing transfer. However, the nature of coherences has been fiercely debated as coherences only report the energy gap between the states that generate coherence signals. Recent works have suggested that either the coherences observed in photosynthetic antenna complexes arise from vibrational wave packets on the ground state or, alternatively, coherences arise from mixed electronic and vibrational states. Understanding origin of coherences is important for designing molecules for efficient light harvesting. Here, we give a direct experimental observation from a mutant of LH2, which does not have B800 chromophores, to distinguish between electronic, vibrational, and vibronic coherence. We also present a minimal theoretical model to characterize the coherences both in the two limiting cases of purely vibrational and purely electronic coherence as well as in the intermediate, vibronic regime.

Communication: Coherences observed in vivo in photosynthetic bacteria using two-dimensional electronic spectroscopy

Abstract: Energy transfer through large disordered antenna networks in photosynthetic organisms can occur with a quantum efficiency of nearly 100% This energy transfer is facilitated by the electronic structure of the photosynthetic antennae as well as interactions between electronic states and the surrounding environment Coherences in time-domain spectroscopy provide a fine probe of how a system interacts with its surroundings In two-dimensional electronic spectroscopy, coherences can appear on both the ground and excited state surfaces revealing detailed information regarding electronic structure, system-bath coupling, energy transfer, and energetic coupling in complex chemical systems Numerous studies have revealed coherences in isolated photosynthetic pigment-protein complexes, but these coherences have not been observed in vivo due to the small amplitude of these signals and the intense scatter from whole cells Here, we present data acquired using ultrafast video-acquisition gradient-assisted photon echo spectroscopy to observe quantum beating signals from coherences in vivo Experiments were conducted on isolated light harvesting complex II (LH2) from Rhodobacter sphaeroides, whole cells of R sphaeroides, and whole cells of R sphaeroides grown in 30% deuterated media A vibronic coherence was observed following laser excitation at ambient temperature between the B850 and the B850∗ states of LH2 in each of the 3 samples with a lifetime of ∼40-60 fs

Gadolinium nicotinate clusters as potential MRI contrast agents

Abstract: Three multinuclear gadolinium(III) clusters containing the nicotinate (nic) ligand, [Gd2(nic)6(H2O)4] (1), [Gd4(μ3-OH)4(Hnic)5(H2O)12](ClO4)8·7H2O (2), and [Gd4(μ3-OH)4(nic)6(H2O)6]2(ClO4)4·4H2O (3) were synthesized and characterized. Potential applications of these Gd(III) clusters as high-field magnetic resonance imaging (MRI) contrast agents were evaluated. The longitudinal relaxivities (r1) of 1–3 in water at 7 T were determined to be 10.45 ± 0.16, 9.28 ± 0.06, and 2.04 ± 0.29 mM−1 s−1 on a per Gd ion basis, respectively. In 1% agarose solution, the r1 values increased slightly to 10.37 ± 0.31, 10.74 ± 0.11, and 4.60 ± 0.29 mM−1 s−1 for 1–3, respectively. The ability to tune the number of inner-sphere water molecules, cluster sizes, organic ligands, and Gd coordination modes in such Gd(III) clusters provide interesting opportunities to further enhance the MR relaxivities for potential MRI applications.