Microwave-Mediated Synthesis of Bulky Lanthanide Porphyrin–Phthalocyanine Triple-Deckers: Electrochemical and Magnetic Properties

Five heteroleptic lanthanide porphyrin–bis-phthalocyanine triple-decker complexes with bulky peripheral groups were prepared via microwave-assisted synthesis and characterized in terms of their spectroscopic, electrochemical, and magnetic properties. These compounds, which were easily obtained under our preparative conditions, would normally not be accessible in large quantities using conventional synthetic methods, as a result of the low yield resulting from steric congestion of bulky groups on the periphery of the phthalocyanine and porphyrin ligands. The electrochemically investigated triple-decker derivatives undergo four reversible one-electron oxidations and three reversible one-electron reductions. The sites of oxidation and reduction were assigned on the basis of redox potentials and UV–vis spectral changes during electron-transfer processes monitored by thin-layer spectroelectrochemistry, in conjunction with assignments of electronic absorption bands of the neutral compounds. Magnetic susceptibility measurements on two derivatives containing Tb^III and Dy^III metal ions reveal the presence of ferromagnetic interactions, probably resulting from magnetic dipolar interactions. The Tb^III derivative shows SMM behavior under an applied field of 0.1 T, where the direct and Orbach process can be determined, resulting in an energy barrier of <i>U</i>_eff = 132.0 K. However, Cole–Cole plots reveal the presence of two relaxation processes, the second of which takes place at higher frequencies, with the data conforming to a 1/<i>t</i> ∝ <i>T</i>⁷ relation, thus suggesting that it can be assigned to a Raman process. Attempts were made to form two-dimensional (2D) self-assembled networks on a highly oriented pyrolytic graphite (HOPG) surface but were unsuccessful due to bulky peripheral groups on the two Pc macrocycles

Anisotropic Organization and Microscopic Manipulation of Self-Assembling Synthetic Porphyrin Microrods That Mimic Chlorosomes: Bacterial Light-Harvesting Systems

Being able to control in time and space the positioning, orientation, movement, and sense of rotation of nano- to microscale objects is currently an active research area in nanoscience, having diverse nanotechnological applications. In this paper, we demonstrate unprecedented control and maneuvering of rod-shaped or tubular nanostructures with high aspect ratios which are formed by self-assembling synthetic porphyrins. The self-assembly algorithm, encoded by appended chemical-recognition groups on the periphery of these porphyrins, is the same as the one operating for chlorosomal bacteriochlorophylls (BChl's). Chlorosomes, rod-shaped organelles with relatively long-range molecular order, are the most efficient naturally occurring light-harvesting systems., They are used by green photosynthetic bacteria to trap visible and infrared light of minute intensities even at great depths, e.g., 100 m below water surface or in volcanic vents in the absence of solar radiation. In contrast to most other natural light-harvesting systems, the chlorosomal antennae are devoid of a protein scaffold to orient the BChl's; thus, they are an attractive goal for mimicry by synthetic chemists, who are able to engineer more robust chromophores to self-assemble. Functional devices with environmentally friendly chromophoreswhich should be able to act as photosensitizers within hybrid solar cells, leading to high photon-to-current conversion efficiencies even under low illumination conditionshave yet to be fabricated. The orderly manner in which the BChl's and their synthetic counterparts self-assemble imparts strong diamagnetic and optical anisotropies and flow/shear characteristics to their nanostructured assemblies, allowing them to be manipulated by electrical, magnetic, or tribomechanical forces

Anisotropic Organization and Microscopic Manipulation of Self-Assembling Synthetic Porphyrin Microrods That Mimic Chlorosomes: Bacterial Light-Harvesting Systems

Being able to control in time and space the positioning, orientation, movement, and sense of rotation of nano- to microscale objects is currently an active research area in nanoscience, having diverse nanotechnological applications. In this paper, we demonstrate unprecedented control and maneuvering of rod-shaped or tubular nanostructures with high aspect ratios which are formed by self-assembling synthetic porphyrins. The self-assembly algorithm, encoded by appended chemical-recognition groups on the periphery of these porphyrins, is the same as the one operating for chlorosomal bacteriochlorophylls (BChl's). Chlorosomes, rod-shaped organelles with relatively long-range molecular order, are the most efficient naturally occurring light-harvesting systems., They are used by green photosynthetic bacteria to trap visible and infrared light of minute intensities even at great depths, e.g., 100 m below water surface or in volcanic vents in the absence of solar radiation. In contrast to most other natural light-harvesting systems, the chlorosomal antennae are devoid of a protein scaffold to orient the BChl's; thus, they are an attractive goal for mimicry by synthetic chemists, who are able to engineer more robust chromophores to self-assemble. Functional devices with environmentally friendly chromophoreswhich should be able to act as photosensitizers within hybrid solar cells, leading to high photon-to-current conversion efficiencies even under low illumination conditionshave yet to be fabricated. The orderly manner in which the BChl's and their synthetic counterparts self-assemble imparts strong diamagnetic and optical anisotropies and flow/shear characteristics to their nanostructured assemblies, allowing them to be manipulated by electrical, magnetic, or tribomechanical forces