Natural light-harvesting systems absorb sunlight and transfer its energy to the reaction centre, where it is used for photosynthesis. Synthetic chromophore arrays provide useful models for understanding energy migration in these systems. Research has focussed on mimicking rings of chlorophyll molecules found in purple bacteria, known as 'lightharvesting system 2'. Linear meso-meso linked porphyrin chains mediate rapid energy migration, but until now it has not been possible to bend them into rings. Here we show that oligo-pyridyl templates can be used to bend these rod-like photonic wires to create covalent nanorings that consist of 24 porphyrin units and a single butadiyne link. Their elliptical conformations have been probed by scanning tunnelling microscopy. This system exhibits two excited state energy transfer processes: one from a bound template to the peripheral porphyrins and one, in the template-free ring, from the exciton-coupled porphyrin array to the π-conjugated butadiyne-linked porphyrin dimer segment.Green plants, and other photosynthetic organisms, capture sunlight using antenna complexes that consist of large arrays of chlorophyll molecules. Electronic excitation is funnelled through the antenna complex into a reaction centre, where it is converted into chemical energy 1,2 . There are typically 100-800 light-absorbing chlorophyll units per reaction centre 3 , and each absorption event results in a long cascade of electronic excitation energy transfer (EET) steps. Light harvesting systems have evolved so that this EET process is
Intra-atomic correlation and surface effects on the charge states of protons moving in an electron gas have been analysed in this paper. Our main conclusion is that surface effects are of primary importance to the understanding of the experimental charge fractions of protons moving at low velocities. By means of a simple model, we have shown that proton velocities can be correlated with those effective electron densities determining the charge states of protons.
Impregnation of phosphine-decorated styrene-based Polymer Immobilized Ionic Liquid (PPh2-PIIL) with ruthenium (III) trichloride resulted in facile reduction of the ruthenium to afford Ru(II) impregnated phosphine oxide-decorated PIIL (O=PPh2PIIL). The derived...
Graphene nanoribbons (GNRs), nanometer-wide strips of graphene, are promising materials for fabricating electronic devices. Many GNRs have been reported, yet no scalable strategies are known for synthesizing GNRs with metal atoms and heteroaromatic units at precisely defined positions in the conjugated backbone, which would be valuable for tuning their optical, electronic and magnetic properties. Here, we report the first solution-phase synthesis of a porphyrin-fused graphene nanoribbon (PGNR). This PGNR has metalloporphyrins fused into a twisted fjord-edged GNR backbone; it consists of long chains (>100 nm), with a narrow optical bandgap (~1.0 eV) and extraordinarily high local charge mobility (>400 cm2 V–1 s–1 by Terahertz spectroscopy). It has been used to fabricate ambipolar field-effect transistors with appealing switching behavior, and single-electron transistors displaying multiple Coulomb diamonds. These results open an avenue to PGNRs with engineerable electrical and magnetic properties, transposing the coordination chemistry of porphyrins into π-extended nanostructures.
Rings of porphyrins mimic natural lightharvesting chlorophyll arrays and offer insights into electronic delocalization, providing a motivation for creating larger nanorings with closely spaced porphyrin units. Here, we demonstrate the first synthesis of a macrocycle consisting entirely of 5,15-linked porphyrins. This porphyrin octadecamer was constructed using a covalent six-armed template, made by cobalt-catalyzed cyclotrimerization of an H-shaped tolan with porphyrin trimer ends. The porphyrins around the circumference of the nanoring were linked together by intramolecular oxidative meso-meso coupling and partial β-β fusion, to give a nanoring consisting of six edge-fused zinc(II) porphyrin dimer units and six un-fused nickel(II) porphyrins. STM imaging on a gold surface confirms the size and shape of the spoked 18-porphyrin nanoring (calculated diameter: 4.7 nm).
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