Supramolecular squares of porphyrazines

The design, self-assembly, and characterization of discrete arrays of porphyrazine (Pz) squares are presented to illustrate the supramolecular chemistry of these macrocycles, and to highlight that these arrays have physical chemical properties that are different from similar arrays of porphyrinic systems.     

Porphyrins linked directly to the 5,5' positions of 2,2'-bipyridine: a new supramolecular building block and switch

The synthesis and coordination chemistry of two porphyrin dimers linked either at the 5,5' or the 4,4' positions of 2,2'-bipyridine are described. These compounds, which may serve a molecular tectons for the constructions of a variety of supramolecular arrays of diverse function, reveal that the ground- and excited-state electronic communication between the chromophores is only moderately affected by the complexation state of the bipyridyl moiety. The nature of the metal ion chelated by the bipyridine only slightly perturbs the ground-state spectra, and differences observed in the excited state are largely ascribed to the heavy atom effect. This work also shows that conformational changes in structural subunits, in this case induced by bipyridyl complexation of various metal ions, do not necessarily require reorganization of supramolecular systems.     

Synthesis of Linear Amphipathic Porphyrin Dimers and Trimers: An Approach to Bilayer Lipid Membrane Spanning Porphyrin Arrays

A modular building-block approach has been developed for the construction of linear amphipathic porphyrin arrays. The reaction of meso-(trifluoromethyl)dipyrromethane and an aldehyde under the conditions of the two-step room temperature porphyrin synthesis affords the trans-substituted porphyrin (13-56% yields). A similar reaction with two different aldehydes provides access to porphyrins bearing two different functional groups. An ethyne porphyrin and an iodo porphyrin (either free base or zinc) are selectively joined via Pd(0)-catalyzed coupling reactions, affording a linear array with porphyrins in defined metalation states. Coupling of a zinc-porphyrin bearing iodo and ester groups with a free base porphyrin bearing ethyne and ester groups yielded the zinc-free base porphyrin dimer. Coupling of a bis-ethyne porphyrin with a porphyrin bearing iodo and ester groups afforded the porphyrin trimer. Cleavage of the esters yielded the amphipathic porphyrin dimer and trimer arrays. The arrays with adjacent zinc and free base porphyrins undergo efficient electronic energy transfer. Both amphipathic porphyrin arrays have been incorporated into L-alpha-phosphatidylcholine vesicles. This versatile synthetic strategy provides access to a family of porphyrin arrays for studies of photophysical processes in supramolecular assemblies.     

Metal-mediated Discrete Supramolecular Assemblies of Porphyrins

There is substantial recent interest worldwide in the construction of multiporphyrin assemblies which can either mimic naturally occurring multichromophore aggregates, such as the photosynthetic reaction center and the light harvesting complex of purple bacteria, or which can be used as electron- and/or energy-transfer molecular devices for advanced technological tasks. The metal-mediated self-assembly approach, which exploits the formation of coordination bonds between peripheral basic site(s) on the porphyrins and metal centers, has recently allowed the design and preparation of sophisticated supramolecular architectures whose complexity and function begin to approach the properties of naturally occurring systems. Within this framework, meso -pyridyl/phenyl porphyrins (PyPs), or strictly related chromophores, can provide geometrically well-defined connections to as many as four metal centers by coordination of the pyridyl groups. Several discrete assemblies of various nuclearities, in which the pyridylporphyrins are linkers binding metalloporphyrins and/or coordination compounds, have been constructed in recent years. Our contribution to this field is reviewed, with the aim of providing insight into the design of new, more elaborated architectures of higher order.     

meso-四(4-N-甲基吡啶基)卟啉-金属-氧簇超分子化合物的光谱及电催化氧还原行为研究

采用紫外可见吸收光谱研究了meso -四 ( 4 -N -甲基吡啶基 )卟啉 (M1 TMPyP ,M1 =H2 ,Zn)阳离子与金属-氧簇阴离子 (SiW1 2 O40 4 - )在水溶液中的光谱行为 .光谱演变及Job′s图表明M1 TMPyP与SiW1 2 O40 4 - 在水溶液中可形成相对稳定的 1∶1的超分子化合物。溶液的紫外可见吸收谱图明显不同于未相互作用的反应物吸收谱图的加和 ,表明有新化合物生成 ,且卟啉的发色团与SiW1 2 O40 4 - 通过静电发生强相互作用 ,同时考察了化学计量为1∶1的 [CoTMPyP][SiW1 2 O40 ]超分子化合物的电催化氧还原活性及其稳定性 ,表明该类超分子化合物有望成为新一类的催化氧还原的修饰电极材料。     

Giant multiporphyrin arrays as artificial light-harvesting antennas

Synthetic giant multiporphyrin arrays with well-defined architectures are reviewed in terms of artificial light-harvesting materials. Meso,meso-linked porphyrin arrays and multiporphyrin dendrimers have successfully mimicked the light-harvesting function of bacterial photosynthetic systems. We have also developed novel multiporphyrin-modified metal nanoclusters where porphyrins employed as a light-harvesting unit are well organized onto metal nanoclusters by self-assembly processes. Multiporphyrin-modified metal nanoclusters have been applied to photocatalyses and photovoltaic cells. In particular, they have been assembled with fullerenes step-by-step to make large, uniform clusters on nanostructured semiconductor electrodes, which exhibit a high power-conversion efficiency close to 1%. These systems provide valuable information on the design of porphyrin molecular assemblies that can be tailored to construct molecular photonic devices as well as artificial photosynthetic systems.     

Chemical models for aspects of the photosynthetic reaction centre: synthesis and photophysical properties of tris- and tetrakis-porphyrins that resemble the arrangement of chromophores in the natural system

Tris-porphyrin and tetrakis-porphyrin arrays 1 and 2 are proposed as models for the arrangement of the chromophores that constitute photosynthetic reaction centres (PRC's). Their porphyrinic chromophores are similar in distance apart to the key chromophores of PRC's and the C2 symmetric arrangement of the macrocycles that constitute the 'special pair' where charge separation occurs is also incorporated. The use of zinc(II) and gold(III) chelation establishes an energy gradient for photoinduced electron transfer across each compound. Synthesis was achieved in good yields through a strategy that used the construction of biquinoxalinyl and Tr?ger's base linkages between the porphyrinoid components. Compounds which are bis-porphyrin molecular components of the arrays were also synthesised. Photophysical analyses indicate that long-range photoinduced energy and electron transfer processes occur in the extended arrays in addition to those occurring in the component bis-porphyrins. Evidence for step-wise electron transfer between terminal zinc(II)-chelated and gold(III)-chelated porphyrins has been detected in both porphyrins 1 and 2 in polar solvents, representing charge transfer across 35 A and 50 A, respectively. At 298 K, in deaerated benzonitrile, the lifetime of the charge transfer state of the tris-porphyrin 1 is 150 ns and the lifetime of the charge transfer state of tetrakis-porphyrin 2 is 59.4 micros; very long when compared to simpler chemical model systems, but still much shorter than the 1 s lifetime of the charge separated state of natural PRC's in cell membranes.     

Binding sites on the outside of metallo-supramolecular architectures; engineering coordination polymers from discrete architectures

Aggregation of metallo-supramolecular architectures through additional coordination is explored by introducing metal-binding units onto the outside of the supramolecular architectures. This is achieved within the framework of our imine-based approach to supramolecular architecture, by replacing the pyridylimine units with pyrazylketimine units. An advantage of the design is that it retains the ease-of-synthesis which characterises our imine-based approach. Silver(I) complexes of three pyrazylketimine ligand systems are described. The complexes demonstrate that introducing pyrazine donor units does indeed allow higher-order assembly of the distinct supramolecular architectures into engineered coordination polymers. Two distinct types of aggregation are observed. In the first, the donors on the outside of one architecture bind to the metals of another to link the units into a polymeric array. In the second type, the donors on the outside of the architectures bind to separate metal centres which are themselves not part of the architectures, and these separate metal centres link the units to form the macromolecular array. The weaker donor nature of the pyrazine nitrogens (compared to pyridine) also introduces an additional element into the design; higher coordination numbers are favoured and this can lead to arrays with higher connectivity than those observed in the discrete pyridylimine architectures.     

Planar meso pentafluorophenyl core modified isophlorins

Isophlorins and its analogues bridge the structural features between porphyrins and annulenes. Invariably they are known to be unstable but can be stabilized by appropriate substituents in the core and periphery of a macrocycle. Solid-state characterization of these 20pi systems displays planarity for each macrocycle and even in their supramolecular arrangement due to C-H...F-C interactions.     

Helical polymer-anchored porphyrin nanorods

Well-defined arrays of porphyrins attached to a rigid polyisocyanide backbone have been synthesized and their physical and optical properties studied. The helical polymers are rigidified by an inter-side chain hydrogen-bonded network and have an average mass of 1.1 x 10(6) Daltons and a polydispersity index of 1.3. Each of the polymer strands contains four columns of around 200 stacked porphyrins and has an overall length of 87 nm. The chromophores are arranged in a left-handed helical fashion along the polymer backbone. Photophysical studies show that at least 25 porphyrins within one column are excitationally coupled.     

Supramolecular Clippers for Controlling Photophysical Processes through Preorganized Chromophores

A novel supramolecular clipping design for influencing the photophysical properties of functional molecular assemblies, by the preorganization (clipping) of chromophores, is described. Several chromophores end functionalized with molecular recognition units were designed. These molecular recognition units serve as handles to appropriately position these systems upon noncovalent interactions with multivalent guest molecules (supramolecular clippers). Towards this goal, we have synthesized 1,5‐dialkoxynaphthalene (DAN) and naphthalenediimide (NDI) functionalized with dipicolylethylenediamine (DPA) motifs. These molecules could preorganize upon noncovalent clipping with adenosine di‐ or triphosphates, which resulted in preassociated excimers and mixed (cofacial) charge‐transfer (CT) assemblies. Chiral guest binding could also induce supramolecular chirality, not only into the individual chromophoric assembly but also into the heteromeric CT organization, as seen from the strong circular dichroism (CD) signal of the CT transition. The unique ability of this design to influence the intermolecular interactions by changing the binding strength of the clippers furthermore makes it very attractive for controlling the bimolecular photophysical processes.     

Photoactive metallocyclodextrins: sophisticated supramolecular arrays for the construction of light activated miniature devices

The introduction of photoactive metal centres onto cyclodextrin receptors opens up new possibilities for the design of sensors, wires and energy conversion systems. This tutorial review focuses on strategies involving such metallocyclodextrins for the construction of supramolecular arrays with light-activated functions. The assembly procedures for building such arrays are presented, together with the features required for their functions both as sensors for ion or small molecule detection and as wires for photoinduced long-range energy or electron transport. Systems for metal ion sensing are described where the cyclodextrin plays a mediating role in influencing the luminescence properties of an organic probe, responsive to metal binding. Small molecule sensing by the cyclodextrin cavity is realised using luminescent lanthanide or transition metal functionalised cyclodextrins. The light signal of the photoactive metal is switched on or off upon binding an analyte in the cyclodextrin cavity. The metallocyclodextrin systems that function as wires are distinguished by the controlled assembly of transition metal polypyridine and metalloporphyrin units. These units have inherent photoactivity that defines the vectorial direction of energy or electron transfer processes through the wire.     

Grid-type metal ion architectures: functional metallosupramolecular arrays

Recent advances in supramolecular coordination chemistry allow access to transition-metal complexes of grid-type architecture comprising two-dimensional arrays of metal ions connecting a set of organic ligands in a perpendicular arrangement to generate a multiple wiring network. General design principles for these structures involve the thermodynamically driven synthesis of complex discrete objects from numerous molecular components in a single overall operation. Such supramolecular metal ion arrays combine the properties of their constituent metal ions and ligands, showing unique optical, electrochemical, and magnetic behavior. These features present potential relevance for nanotechnology, particularly in the area of supramolecular devices for information storage and processing. Thus, a dense organization of addressable units is represented by an extended "grid-of-grids" arrangement, formed by interaction of grid-type arrays with solid surfaces.     

Design,Synthesis, and Properties of Molecule-Based Assemblies with Large Second-Order Optical Nonlinearities

The design, synthesis, characterization, and understanding of new molecular and macromolecular assemblies with large macroscopic optical nonlinearities represents an active field of research at the interface of modern chemistry, physics, and materials science. Challenges in this area of photonic materials typify an important theme in contemporary chemistry: to create new types of functional materials by the rational construction of supramolecular assemblies exhibiting preordained collective phenomena by virtue of “engineered” molecule–molecule interactions and spatial relationships. This review surveys several approaches to, and the microstructural and optical properties of, second-order nonlinear optical materials built from noncentrosymmetric assemblies of chromophores having large molecular hyperpolarizabilities. Such types of materials can efficiently double the frequency of incident light, exhibit other second-order nonlinear optical effects, and contribute to the knowledge base needed for new photonic device technologies. Systems described include chromophore macromolecule guesthost matrices, chromophore-functionalized glassy macromolecules, thermally crosslinked chromophore-macromolecule matrices, and intrinsically acentric self-assembled chromophoric superlattices.     

Mechanisms, pathways, and dynamics of excited-state energy flow in self-assembled wheel-and-spoke light-harvesting architectures

Static and time-resolved optical measurements are reported for two cyclic hexameric porphyrin arrays and their self-assembled complexes with guest chromophores. The hexameric hosts contain zinc porphyrins and 0 or 3 free base (Fb) porphyrins (denoted Zn(6) or Zn(3)Fb(3), respectively). The guests are a tripyridyl arene (TP) and a dipyridyl-substituted free base porphyrin (DPFb), each of which coordinates to zinc porphyrins of a host via pyridyl-zinc dative bonding. Each architecture is designed to have an overall gradient of excited-state energies that affords excitation funneling within the host and ultimately to the guest. Collectively, the studies delineate the various pathways, mechanisms, and rate constants of energy flow among the weakly coupled constituents of the host-guest complexes. The pathways include downhill unidirectional energy transfer between adjacent chromophores, bidirectional energy migration between identical chromophores, and energy transfer between nonadjacent chromophores. The energy transfer to the lowest-energy chromophore(s) within the backbone of a hexameric host (Fb porphyrins in Zn(3)Fb(3) or pyridyl-coordinated zinc porphyrins in Zn(6)*TP and Zn(6)*DPFb) proceeds primarily via a through-bond mechanism; the transfer is rapid (approximately 40 ps depending on the array) and essentially quantitative (>or=98%). The energy transfer from a pyridyl-coordinated zinc porphyrin of the host to the Fb porphyrin guest in the Zn(6)*DPFb complex is almost exclusively F?rster through-space in nature; this process is much slower ( approximately 1 ns) and has a lower yield (65%). These studies highlight the utility of cyclic architectures for efficient light harvesting and energy transfer to a designated trapping site.     

卟啉超分子的组装合成及其应用新进展

卟啉超分子已被广泛地用于光学、催化、仿生等方面的研究,部分研究成果已获得实际应用．本文综述了卟啉超分子在组装合成及应用方面的新进展,包括基于不同结构卟啉砌块的新型二维与三维超分子的构筑以及卟啉超分子在光学、催化和分子识别等方面的应用．     

Cover Picture

The cover picture shows a schematic representation of a supramolecular rod composed of meso-meso-coupled porphyrins. The Ag(I)-promoted meso-meso coupling of Zn(II) 5,15-diarylporphyrins enabled regularly arranged arrays with 2-128 porphyrins to be assembled. An examination of the absorption spectra of these rods show that they all exhibit split Soret bands as a result of exciton coupling. As the number of porphyrins increases the low-energy Soret band is shifted to longer wavelength while the high-energy Soret band stays at nearly the same wavelength, which results in a progressive increase in the splitting energy. A study of the fluorescence spectra of the arrays shows the S(1) states are delocalized over 6-8 porphyrin units. The 128mer at 0.1-μm long is the longest monodisperse, rodlike molecule so far known, and should, together with the smaller arrays, have the potential for application as light-harvesting wires. Further details are reported by A. Osuka et al. on p. 1458 ff.[ Magnified Cover Picture ]     

Synthesis of new luminescent supramolecular assemblies from fluorenyl porphyrins and polypyridyl isocyanurate-based spacers

Two new dendrimeric supramolecular assemblies bearing twelve and twenty-four fluorenyl peripheral donor groups surrounding an organic core have been prepared and studied. These assemblies are composed of three zinc porphyrins possessing each four (ZnTFP) and eight fluorenyl chromophores (ZnOOFP) linked together by a central tris-pyridyl organic ligand. Due to efficient energy transfer between the fluorenyl arms, which act as antennas, and the Zn centres, which act as emitters; these assemblies behave as red emitters after selective UV or visible irradiation. The kinetic stability of these supramolecular assemblies and its impact on their photophysical properties are discussed.     

Differential receptor arrays and assays for solution-based molecular recognition

Nature has inspired an emergent supramolecular field of synthetic receptor arrays and assays for the pattern-based recognition of various bioanalytes and metal species. The synthetic receptors are not necessarily selective for a particular analyte, but the combined signal response from the array is diagnostic for the analyte. This tutorial review describes recent work in the literature for this emerging supramolecular field and details basic array and assay design principles. We review the analytes targeted, signaling types used, and pattern recognition.Developing specific receptors for the solution-based analysis of complex analytes and mixtures is a daunting task. A solution to this difficult task has been inspired by nature's use of arrays of receptors in the senses of taste and smell. An emerging field within supramolecular chemistry is the use of synthetic and readily available receptors in array formats for the detection of analytes in solution. Each receptor in a differential array does not necessarily have selectivity for a particular analyte, but the combined fingerprint response can be extracted as a diagnostic pattern visually, or using chemometric tools. This new genre of molecular recognition is advancing rapidly with several groups developing novel array platforms and receptors.