Giant porphyrin disks: control of their self-assembly at liquid-solid interfaces through metal-ligand interactions

The synthesis and self-assembly behaviour of porphyrin dodecamers 1H(2) and Zn-1, which consist of twelve porphyrins that are covalently attached to a central aromatic core, is described. According to STM, 1D and 2D NMR studies, and molecular modelling calculations, the porphyrin dodecamers have a yo-yo-shaped structure. Their large pi surface, in combination with their disk-like shape, allows them to form self-assembled structures, which in the case of Zn-1 can be tuned by adding bidentate ligands. The self-assembly of the molecules at the liquid-solid interface of 1-phenyloctane with highly oriented pyrolytic graphite or Au(111) was imaged by using STM. The porphyrin disks in the self-assembled arrays have an edge-on orientation on the surface. The addition of bidentate axial ligands to the Zn-1 molecules in the arrays allows their intermolecular distance to be precisely controlled.     

From supramolecular porphyrin tweezers to dynamic A(n)B(m)C(l)D(k) multiporphyrin arrangements through orthogonal coordination

A dynamic, supramolecular, three-component A(n)B(m)C(l) bis(zinc porphyrin) tweezer has been prepared quantitatively using the heteroleptic bisphenanthroline (HETPHEN) concept. Upon addition of nitrogenous spacers of different length, namely, the extended bipyridine 3 a, 4,4'-bipyridine (3 b), and 1,4-diazabicyclo[2.2.2]octane (DABCO; 3 c), to set up an additional orthogonal binding motif (Zn(Por)-N(spacer)), three structurally different, still dynamic, four-component A(n)B(m)C(l)D(k) assemblies were cleanly formed, as indicated by UV/Vis and NMR titrations as well as by DOSY investigations. The structures were identified as a bridged monotweezer A(2)BC(2)D, a doubly bridged double tweezer A(4)B(2)C(4)D(2), and a triply bridged double tweezer A(4)B(2)C(4)D(3), the latter resembling a porphyrin stack. Notably, the same structures were equally formed directly from a mixture of the constituents A, B, C, and D put together in any sequence if the correct stoichiometry was applied.     

Large-scale controllable patterning growth of aligned organic nanowires through evaporation-induced self-assembly

Organic one-dimensional nanostructures are attractive building blocks for electronic, optoelectronic, and photonic applications. Achieving aligned organic nanowire arrays that can be patterned on a surface with well-controlled spatial arrangement is highly desirable in the fabrication of high-performance organic devices. We demonstrate a facile one-step method for large-scale controllable patterning growth of ordered single-crystal C(60) nanowires through evaporation-induced self-assembly. The patterning geometry of the nanowire arrays can be tuned by the shape of the covering hats of the confined curve-on-flat geometry. The formation of the pattern arrays is driven by a simple solvent evaporation process, which is controlled by the surface tension of the substrate (glass or Si) and geometry of the evaporation surface. By sandwiching a solvent pool between the substrate and a covering hat, the evaporation surface is confined to along the edge of the solvent pool. The geometry of the formed nanowire pattern is well defined by a surface-tension model of the evaporation channel. This simple method is further established as a general approach that is applicable to two other organic nanostructure systems. The I-V characteristics of such a parallel, organic, nanowire-array device was measured. The results demonstrate that the proposed method for direct growth of nanomaterials on a substrate is a feasible approach to device fabrication, especially to the fabrication of the parallel arrays of devices.     

Selective inclusion of electron-donating molecules into porphyrin nanochannels derived from the self-assembly of saddle-distorted, protonated porphyrins and photoinduced electron transfer from guest molecules to porphyrin dications

A doubly protonated hydrochloride salt of a saddle-distorted dodecaphenylporphyrin (H2DPP), [H4DPPP]Cl2, forms a porphyrin nanochannel (PNC). X-ray crystallography was used to determine the structure of the molecule, which revealed the inclusion of guest molecules within the PNC. Electron-donating molecules, such as p-hydroquinone and p-xylene, were selectively included within the PNC in sharp contrast to electron acceptors, such as the corresponding quinones, which were not encapsulated. This result indicates that the PNC can recognize the electronic character and steric hindrance of the guest molecules during the course of inclusion. ESR measurements (photoirradiation at lambda>340 nm at room temperature) of the PNC that contains p-hydroquinone, catechol, and tetrafluorohydroquinone guest molecules gave well-resolved signals, which were assigned to cation radicals formed without deprotonation based on results from computer simulations of the ESR spectra and density functional theory (DFT) calculations. The radicals are derived from photoinduced electron transfer from the guest molecules to the singlet state of H4DPP2+. Transient absorption spectroscopy by femtosecond laser flash photolysis allowed us to observe the formation of 1(H4DPP2+)*, which is converted to H4DPP+. by electron transfer from the guest molecules to 1(H4DPP2+)*, followed by fast disproportionation of H4DPP+., and charge recombination to give diamagnetic species and the triplet excited state 3(H4DPP2+)*, respectively.     

Supramolecular Nanoassemblies of an Amphiphilic Porphyrin–Cyclodextrin Conjugate and Their Morphological Transition from Vesicle to Network

An amphiphilic compound, 5‐(4′‐dodecyloxyphenyl)‐10,15,20‐tri(permethyl‐β‐CD)‐modified Zn^II–porphyrin ( 1 ; β‐CD=β‐cyclodextrin), was synthesized by means of the click reaction of an alkylated Zn–porphyrin derivative with 6‐deoxy‐6‐azidopermethyl‐β‐CD. The complexation between 1 and tetrasodium tetraphenylporphyrintetrasulfonate ( 5 ) with different molar ratios led to the formation of two distinctly different nanoarchitectures, which were proven to be vesicle and network aggregates, respectively, by using dynamic light scattering, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. On the basis of the results of the time‐dependent TEM studies, fluorescence, and NMR spectroscopic measurements, we have determined that the mechanism of the morphology transition from vesicles to networks is controlled by the stepwise complexation of 1 with 5 . Furthermore, these supramolecular nanoarchitectures show the controlled‐ release property of doxorubicin as potential candidates for drug delivery.     

Controlled self-assembly of amphiphilic oligopeptides into shape-specific nanoarchitectures

Here, we report a novel, programmable, molecular self-assembling system to fabricate shape-specific, three-dimensional nanoarchitectures. Three types of simple 16-mer peptides consisting of hydrophobic Leu and hydrophilic Lys, LKL16, KLK16, and LK16, were prepared as building blocks for nanofabrications. A detailed analysis of the conformation and self-assembling mechanism was performed by using circular dichroism (CD), FTIR spectroscopy, and atomic force microscopy (AFM). A wide variety of self-assembled nanoarchitectures, such as beta-sheet-plates, beta-sheet-fibers, alpha-helix-particles, and alpha-helix-plates, could be fabricated by tuning the peptide sequence, reaction time, and solution pH. The ability to control the self-assembled nanostructures should provide a simple and/or essential insight into the mechanism of peptide aggregation, including amyloid formation, and it should be useful for the design of novel bio-related nanomaterials.