Figure‐eight Octaphyrin Bis‐Ge(IV) Complexes: Synthesis,Structures, Aromaticity,and Chiroptical Properties

Highly twisted structures of expanded porphyrin provide a prominent basis to unravel the relationship between aromaticity and chirality. Here we report the synthesis of bis‐Ge(IV) complexes of [38]octaphyrin that display rigid figure‐eight structures. Two bis‐Ge(IV) [38]octaphyrin isomers with respect to the stereochemistry of the axial hydroxy groups on the germanium ions were obtained and found to be aromatic. Upon oxidation with MnO₂, these [38]octaphyrin complexes were converted to a single syn‐type isomer of [36]octaphyrin with retained figure‐eight conformation. The enantiomers have been successfully separated by HPLC equipped with a chiral stationary phase. While aromatic [38]octaphyrin Ge(IV) complexes showed quite large molar circular dichroism of up to Δ?=1500 M^?1cm^?1 with a dissymmetry factor g_abs of 0.035, weakly antiaromatic [36]octaphyrin Ge(IV) complexes underscored moderate values; Δ?=540 M^?1cm^?1 with g_abs of 0.023. Thus, the figure‐eight octaphyrin scaffold has been proved to be an attractive platform for novel chiroptical materials with tunable aromaticity.     

Synthesis of A2B6‐Type [36]Octaphyrins: Copper(II)‐Metalation‐Induced Fragmentation Reactions to Porphyrins and N‐Fusion Reactions of meso‐(3‐Thienyl) Substituents

5,10,15‐Tris(pentafluorophenyl)tetrapyrromethane was efficiently prepared through a route involving stepwise diaroylation of 5‐pentafluorophenyldipyrromethane. A₂B₆‐type [36]octaphyrins were prepared by the cross condensation of the tetrapyrromethane with aryl aldehydes in moderate yields. A₂B₆‐type [36]octaphyrins bearing 2,4,6‐trifluorophenyl, 2,6‐dichlorophenyl, and phenyl substituents underwent Cu^II‐metalation‐induced fragmentation to give two molecules of AB₃‐type Cu^II porphyrins. A₂B₆‐type [36]octaphyrin bearing 3‐thienyl substituents underwent thermal N‐thienyl fusion reactions to provide a modestly aromatic [38]octaphyrin, which, upon treatment with MnO₂, underwent further N‐thienyl fusion and subsequent oxidation to give a nonaromatic doubly N‐thienyl fused [36]octaphyrin.     

Phenylene‐Bridged Core‐Modified Planar Aromatic Octaphyrin: Aromaticity,Photophysical and Anion Receptor Properties

The synthesis of a planar expanded meso porphyrin with an intramolecular para‐phenylene‐bridged core is reported. The planarity of the octaphyrin macrocycle was confirmed by single‐crystal X‐ray structural analysis, in which the bridged para‐phenylene unit deviated by 27° from the mean macrocyclic plane. Spectroscopic analyses and theoretical calculations suggested that the macrocycle was Hückel aromatic and followed a major [34 π] single‐conjugation pathway, which indicated that the bridging para‐phenylene unit was not involved in the macrocyclic conjugation. Analysis of the photophysical properties of this system by steady‐state absorption/fluorescence spectroscopy and transient absorption spectroscopy revealed moderate enhancement in the parameters of the octaphyrin as compared to its non‐bridged octaphyrin congeners, which was attributed to the planarity and rigidity of the macrocycle as imposed by the bridging para‐phenylene unit. Preliminary anion‐binding studies revealed that the protonated macrocycle bound selectively with chloride ions through N?H???Cl hydrogen‐bonding interactions.     

Active Salt/Silica‐Templated 2D Mesoporous FeCo‐Nx‐Carbon as Bifunctional Oxygen Electrodes for Zinc–Air Batteries

Two types of templates, an active metal salt and silica nanoparticles, are used concurrently to achieve the facile synthesis of hierarchical meso/microporous FeCo‐N_x‐carbon nanosheets (meso/micro‐FeCo‐N_x‐CN) with highly dispersed metal sites. The resulting meso/micro‐FeCo‐N_x‐CN shows high and reversible oxygen electrocatalytic performances for both ORR and OER, thus having potential for applications in rechargeable Zn–air battery. Our approach creates a new pathway to fabricate 2D meso/microporous structured carbon architectures for bifunctional oxygen electrodes in rechargeable Zn–air battery as well as opens avenues to the scale‐up production of rationally designed heteroatom‐doped catalytic materials for a broad range of applications.     

Conformational Change from a Twisted Figure‐Eight to an Open‐Extended Structure in Doubly Fused 36π Core‐Modified Octaphyrins Triggered by Protonation: Implication on Photodynamics and Aromaticity

Two examples of core‐modified 36π doubly fused octaphyrins that undergo a conformational change from a twisted figure‐eight to an open‐extended structure induced by protonation are reported. Syntheses of the two octaphyrins (in which Ar=mesityl or tolyl) were achieved by a simple acid‐catalyzed condensation of dipyrrane unit containing an electron‐rich, rigid dithienothiophene (DTT) core with pentafluorobenzaldehyde followed by oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). The single‐crystal X‐ray structure of the octaphyrin (in which Ar=mesityl) shows a figure‐eight twisted conformation of the expanded porphyrin skeleton with two DTT moieties oriented in a staggered conformation with a π‐cloud distance of 3.7 Å. Spectroscopic and quantum mechanical calculations reveal that both octaphyrins conform to a [4n]π nonaromatic electronic structure. Protonation of the pyrrole nitrogen atoms of the octaphyrins results in dramatic structural change, which led to 1) a large redshift and sharpening of absorption bands in electronic absorption spectrum, 2) a large change in chemical shift of pyrrole β‐CH and ? NH protons in the ¹H NMR spectrum, 3) a small increase in singlet lifetimes, and 4) a moderate increase in two‐photon absorption cross‐section values. Furthermore, nucleus‐independent chemical shift (NICS) values calculated at various geometrical positions show positive values and anisotropy‐induced current density (AICD) plots indicate paratropic ring‐currents for the diprotonated form of the octaphyrin (in which Ar=tolyl); the single‐crystal X‐ray structure of the diprotonated form of the octaphyrin shows an extended structure in which one of the pyrrole ring of each dipyrrin subunit undergoes a 180 ° ring‐flip. Four trifluoroacetic acid (TFA) molecules are bound above and below the molecular plane defined by meso‐carbon atoms and are held by N? H ??? O, N? H ??? F, and C? H ??? F intermolecular hydrogen‐bonding interactions. The extended‐open structure upon protonation allows π‐delocalization and the electronic structure conforms to a [4n]π Hückel antiaromatic in the diprotonated state.     

“Protein‐Like” Copolymers: Effect of Polymer Architecture on the Performance in Bioseparation Process

Recently, a new class of copolymers, so‐called protein‐like copolymers has been predicted theoretically by computer simulation. In these copolymers, the conformation of the copolymer determines the exposure of certain comonomer units to the outer solution. Depending on the conformation, copolymer molecules with essentially the same comonomer composition could have pronouncedly different properties. The authors demonstrated experimentally such behavior in case of poly[(N‐vinylcaprolactam)‐co‐(N‐vinylimidazole)] (Dokl. Chem. 2001 , 375, 637). One more group of copolymers with protein‐like behavior is copolymers of N‐isopropylacrylamide with N‐vinylimidazole. Poly[(N‐isopropylacrylamide)‐co‐(N‐vinylimidazole)] was synthesized by radical polymerization and separated into two fractions using immobilized metal affinity chromatography on Cu²⁺‐loaded iminodiacetic acid sepharose CL 6B (Cu²⁺‐IDA‐sepharose). The unbound fraction which passed through the column and bound fraction eluted with Ethylenediaminetetraacetic acid, disodium salt (EDTA) solution differed significantly in molecular weight, 1.4×10⁶ and 1.35×10⁵, respectively but were very close in comonomer composition, 7.8 and 9.1 mol‐% of imidazole, respectively. The composition of bound fraction was confirmed by titration of imidazole groups. Despite close chemical composition, the bound and unbound fraction behaved differently with respect to temperature‐induced phase separation at different pH values, the dependence of hydrodynamic diameter on pH and concentration of Cu²⁺‐ions, and the coprecipitation of soybean trypsin inhibitor with the copolymer in the presence of Cu²⁺‐ions. The differences in the behavior of copolymer fractions are rationalized assuming that the bound fraction presents a protein‐like copolymer.     

N‐Bridged Annulated BODIPYs: Synthesis of Highly Fluorescent Blueshifted Dyes

A series of novel BODIPY dyes has been prepared through the introduction of an N‐bridged annulated meso ‐phenyl ring at one of the β‐positions of the BODIPY core. An unusual blueshift of the main spectral bands is observed, since the fusion of a meso ‐substituent results in a marked relative destabilization of the LUMO. The greater rigidity of the ring‐fused structure leads to very high fluorescence quantum yields. The position of the main spectral bands can be fine‐tuned by introducing electron withdrawing and donating groups onto the meso ‐phenyl ring.     

(5‐tert‐Butylporphyrinato)copper(II), a nonplanar porphyrin with only one sterically demanding meso residue

The title compound, [Cu(C₂₄H₂₀N₄)], is a rare example of a porphyrin carrying only one substituent. Its crystal structure exhibits two molecules in the asymmetric unit. The bulky meso tert‐butyl residue gives rise to a nonplanar macrocycle with significant ruf and sad distortions. As a result of the position of the substituent, the conformational effects are unsymmetric and to a significant extent localized in the affected quadrant of the macrocycle. In line with results for highly substituted nonplanar porphyrins, comparison with a free base and a nickel(II) complex shows that the conformation of the macrocycle is modulated via additional metal effects.     

A photo‐degradable helix: Synthesis,structure, and photolysis of optically active poly[2,7‐bis(4‐t‐butylphenyl)‐9‐methylfluoren‐9‐yl acrylate]

2,7‐Bis(4‐t‐butylphenyl)‐9‐methylfluoren‐9‐yl acrylate ( BBPMFA ) was synthesized and polymerized using α,α′‐azobisisobutyronitrile or n‐Bu₃B‐air as a radical initiator and using the complex of 9‐fluorenyllithium with (S)‐(+)‐1‐(2‐pyrrolidinylmethyl)pyrrolidine as an optically active anionic initiator. Although the radical polymerization led to rather low‐molecular‐weight products at low yields, the anionic polymerization afforded polymers with higher molecular weights in higher yields. The poly( BBPMFA ) obtained by the anionic polymerization was slightly rich in isotacticity (meso diad 57%) and showed an intense circular dichroism (CD) spectrum and large dextrorotation. The intensity of the CD spectrum and magnitude of optical activity increased with an increase in M_n, suggesting that the polymer possesses a preferred‐handed helical conformation. The CD spectrum disappeared within 1 s on irradiation to the polymer in a CHCl₃ solution using a 500‐W Hg‐Xe lamp. This was ascribed to fast photolysis of the ester linkage leading to a loss of helical conformation of the entire chain. Photolysis products of poly( BBPMFA ) were poly(acrylic acid) and 2,7‐bis(4‐t‐butylphenyl)‐9‐methylenefluorene (2,7‐bis(4‐t‐butylphenyl)dibenzofulvene). The photolysis reaction seemed to proceed through the “unzipping” mechanism. The rate constant of photolysis of poly( BBPMFA ) under irradiation at monochromated 325 nm was around 0.01 s^?1 independent of molecular weight. Photolysis at 325 nm was approximately 2400 times faster than that for chemical ester solvolysis under a neutral condition in the dark. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of graft copolymers with “V‐shaped” and “Y‐shaped” side chains via controlled radical and anionic polymerizations

A combination of nitroxide‐mediated radical polymerization and living anionic polymerization was used to synthesize a series of well‐defined graft (co)polymers with “V‐shaped” and “Y‐shaped” branches. The polymer main chain is a copolymer of styrene and p‐chloromethylstyrene (PS‐co‐PCMS) prepared via nitroxide‐mediated radical polymerization. The V‐shaped branches were prepared through coupling reaction of polystyrene macromonomer, carrying 1,1‐diphenylethylene terminus, with polystyryllithium or polyisoprenyllithium. The Y‐shaped branches were prepared throughfurther polymerization initiated by the V‐shaped anions. The obtained branches, carrying a living anion at the middle (V‐shaped) or at the end of the third segment (Y‐shaped), were coupled in situ with pendent benzyl chloride of PS‐co‐PCMS to form the target graft (co)polymers. The purified graft (co)polymers were analyzed by size exclusion chromatography equipped with a multiangle light scattering detector and a viscometer. The result shows that the viscosities and radii of gyration of the branched polymers are remarkably smaller than those of linear polystyrene. In addition, V‐shaped product adopts a more compact conformation in dilute solution than the Y‐shaped analogy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4013–4025, 2007     

meso‐Free BIII Subporphyrins with Electron‐donating Groups

meso‐Free B^III 5,10‐bis(p‐dimethylaminophenyl)subporphyrins were synthesized. They display red‐shifted absorption and fluorescence spectra, bathochromic behaviors in polar solvents, a high fluorescence quantum yield (Φ_F=0.57), and a small HOMO–LUMO gap mainly due to destabilized HOMO as compared with meso‐free B^III 5,10‐diphenylsubporphyrin. This subporphyrin serves as a nice precursor of various meso‐substituted B^III subporphyrins such as B^III meso‐nitrosubporphyrin, B^III meso‐aminosubporphyrin, and meso‐meso’ linked B^III azosubporphyrin dimer. Reactions of meso‐free B^III subporphyrins with NBS or bis(2,4,6‐trimethylpyridine)bromonium hexafluorophosphate gave meso‐meso′ linked subporphyrin dimers, often as a major product along with meso‐bromosubporphyrins.     

Hierarchically Porous Carbons Derived from Metal–Organic Framework/Chitosan Composites for High‐Performance Supercapacitors

Hierarchically porous carbon materials with high surface areas are promising candidates for energy storage and conversion. Herein, the facile synthesis of hierarchically porous carbons through the calcination of metal–organic framework (MOF)/chitosan composites is reported. The effects of the chitosan (CS) additive on the pore structure of the resultant carbons are discussed. The corresponding MOF/chitosan precursors could be readily converted into hierarchically porous carbons (NPC‐V, V=1, 2, 4, and 6) with much higher ratios of meso‐/macropore volume to micropore volume (V_meso‐macro/V_micro). The derived carbon NPC‐2 with the high ratio of V_meso‐macro/V_micro=1.47 demonstrates a high specific surface area of 2375 m² g^?1, and a high pore volume of 2.49 cm³ g^?1, as well as a high graphitization degree, in comparison to its counterpart (NPC) without chitosan addition. These excellent features are favorable for rapid ion diffusion/transport, endowing NPC‐2 with enhanced electrochemical behavior as supercapacitor electrodes in a symmetric electrode system, corresponding to a high specific capacitance of 199.9 F g^?1 in the aqueous electrolyte and good rate capability. Good cycling stability is also observed after 10 000 cycles.     

catena‐Poly[[bis[5‐(4‐pyridyl‐κN)‐2‐(2‐pyridylmethylsulfanyl)‐1,3,4‐oxadiazole]cadmium(II)]‐di‐μ‐thiocyanato‐κ2N:S;κ2S:N]

The title compound, [Cd(NCS)₂(C₁₃H₁₀N₄OS)₂]_n, contains SCN⁻ anions acting as end‐to‐end bridging ligands which utilize both S and N atoms to link cadmium(II) centers into one‐dimensional double chains. The multidentate 5‐(4‐pyridyl)‐2‐(2‐pyridylmethylsulfanyl)‐1,3,4‐oxadiazole ligands behave as monodentate terminal ligands, binding metal centers only through the N atoms of the 4‐pyridyl groups. Two types of eight‐membered rings are formed by two SCN⁻ anions bridging Cd^II centers, viz. planar and chair conformation, which are alternately disposed along the same chain. Finally, chains define a two‐dimensional array through two different interchain π–π stacking interactions.     

Mono‐ and Binuclear Rhodium and Platinum Complexes of 1, 3, 5‐Trimethyl‐1, 3, 5‐triaza‐2σ3λ3‐phosphorin‐4, 6‐dionyloxy‐substituted Calix[4]arenes

The reaction behaviour of 1, 3, 5‐triaza‐2σ³λ³‐phosphorin‐4, 6‐dionyloxy‐substituted calix[4]arenes towards mono‐ and binuclear rhodium and platinum complexes was investigated. Special attention was directed to structure and dynamic behaviour of the products in solution and in the solid state. Depending on the molar ratio of the reactands, the reaction of the tetrakis(triazaphosphorindionyloxy)‐substituted calix[4]arene ( 4 ) and its tert‐butyl‐derivative ( 1 ) with [(cod)RhCl]₂ yielded the mono‐ and disubstituted binuclear rhodium complexes 2 , 3 , and 5 . In all cases, a C₂‐symmetrical structure was proved in solution, apparently caused by a fast intramolecular exchange process between cone conformation and 1, 3‐alternating conformation. The X‐ray crystal structure determination of 5 confirmed [(calixarene)RhCl]₂‐coordination through two opposite phosphorus atoms with a P ⃜P separation of 345 pm. The complex displays crystallographic inversion symmetry, and the Rh₂Cl₂ core is thus exactly planar. Reaction of 1 and of the bis(triazaphosphorindionyloxy)‐bis(methoxy)‐substituted tert‐butyl‐calix‐[4]arene ( 7 ) with (cod)Rh(acac) in equimolar ratio and subsequent reaction with HBF₄ led to the expected cationic monorhodium complexes 5 and 8 , involving 1, 3‐alternating P‐Rh‐P‐coordination. The cone conformation in solution was proved by NMR spectroscopy and characteristic values of the ¹J(PRh) coupling constants in the ³¹P‐NMR‐spectra. Reaction of equimolar amounts of 4 with (cod)Rh(acac) or (nbd)Rh(acac) led, by substitution of the labile coordinated acetylacetonato and after addition of HBF₄, to the corresponding mononuclear cationic complexes 9 and 10 . Only two of the four phosphorus atoms in 9 and 10 are coordinated to the central metal atom. Displacement of either cycloocta‐1, 5‐diene or norbornadiene was not observed. For both compounds, the cone conformation was proved by NMR spectroscopy. Reaction of 4 with (cod)PtCl₂ led to the PtCl₂‐complex ( 11 ). As for all compounds mentioned above, only two phosphorus atoms of the ligand coordinate to platinum, while two phosphorus atoms remain uncoordinated (proved by δ³¹P and characteristic values of ¹J(PPt)). NMR‐spectroscopic evidence was found for the existence of the cone conformation in the cis‐configuration of 11 .     

Nonlinear Optical Properties of Porphyrin Derivatives with Electron‐donating or Electron‐withdrawing Substituents

To investigate photoelectric properties of meso‐extended porphyrin derivatives with electron‐donating or electron‐withdrawing substituents, a series of functionalized porphyrin materials have been designed and synthesized by Suzuki coupling reaction. The meso‐extended structures were fully characterized by ¹H NMR, IR spectroscopy and mass spectrometry. The photophysical properties of porphyrin derivatives were carefully examined by UV‐Visible and fluorescence spectra, and the solvatochromic effect was observed and discussed. In particular, Z‐scan technique was employed to characterize the third‐order nonlinear optical (NLO) properties of the products such as nonlinear absorption and refraction, the third‐order nonlinear refractive indexes (??⁽³⁾‐value) of these porphyrin derivatives achieved 3.9×10^?12 esu. In addition, the compounds could be self‐assembled into highly organized morphologies through phase‐exchange method. All the results indicated that the discotic materials have the potential for optoelectronic applications.     

Synthesis of (bis)Silicon Complexes of [38], [37], and [36]Octaphyrins: Aromaticity Switch and Stable Radical Cation

Silicon complexation of a [38]octaphyrin ( 1 ) was accomplished by reaction with an excess amount of MeSiCl₃ in the presence of N,N‐diisopropylethylamine, thus giving an aromatic [38]octaphyrin bis(silicon) complex 2 . This complex was interconvertible with an antiaromatic [36]octaphyrin congener ( 3 ) by oxidation with MnO₂ and reduction with NaBH₄. Curiously, mild oxidation of 2 with ferrocenium hexafluorophosphate afforded a [37]octaphyrin bis(silicon) complex 4 as an stable radical cation that can be stored under ambient conditions in the solid state. Owing to the two NNNCC‐five‐coordinated Si atoms bearing trigonal bipyramidal geometry, these octaphyrin bis(silicon) complexes take on similar and rigid figure‐of‐eight structures with different consecutive numbers of conjugated π‐electrons (38, 37, and 36), and are all stable.     

Tree‐Bark‐Shaped N‐Doped Porous Carbon Anode for Hydrazine Fuel Cells

Metal‐free N‐doped porous carbon has great potential as a catalyst for hydrazine oxidation in direct hydrazine fuel cells (DHFCs). However, previous studies have reported only half‐cell characterization, and the effect of the pore size distribution has not been intensively investigated. Herein, we report the synthesis of highly active, metal‐free N‐doped carbon (NDC) by controlling the pore size distribution, and for the first time, the effect of the pore size distribution on the anode performance in a DHFC is investigated. As a result, tree‐bark‐shaped NDC with meso /macroporous (>10 nm) structures exhibit a remarkable power density of 127.5 mW cm⁻² in a DHFC.     

Stable Subporphyrin meso‐Aminyl Radicals without Resonance Stabilization by a Neighboring Heteroatom

Most aminyl radicals studied so far are resonance‐stabilized by neighboring heteroatoms, and those without such stabilization are usually short‐lived. We report herein that subporphyrin meso ‐2,4,6‐trichlorophenylaminyl radicals and a bis(5‐subporphyrinyl)aminyl radical are fairly stable under ambient conditions without such stabilization. The subporphyrin meso ‐2,4,6‐trichlorophenylaminyl radical crystal structure displays a characteristically short C_meso −N bond and a perpendicular arrangement of the meso ‐arylamino group. The stabilities of these radicals have been ascribed to extensive spin delocalization over the subporphyrin π‐electronic network as well as steric protection around the aminyl radical center.     

Alkali‐Metal‐Mediated Magnesiations of an N‐Heterocyclic Carbene: Normal,Abnormal, and “Paranormal” Reactivity in a Single Tritopic Molecule

Herein the sodium alkylmagnesium amide [Na₄Mg₂(TMP)₆(nBu)₂] (TMP=2,2,6,6‐tetramethylpiperidide), a template base as its deprotonating action is dictated primarily by its 12 atom ring structure, is studied with the common N‐heterocyclic carbene (NHC) IPr [1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]. Remarkably, magnesiation of IPr occurs at the para‐position of an aryl substituent, sodiation occurs at the abnormal C4 position, and a dative bond occurs between normal C2 and sodium, all within a 20 atom ring structure accommodating two IPr^2?. Studies with different K/Mg and Na/Mg bimetallic bases led to two other magnesiated NHC structures containing two or three IPr^? monoanions bound to Mg through abnormal C4 sites. Synergistic in that magnesiation can only work through alkali‐metal mediation, these reactions add magnesium to the small cartel of metals capable of directly metalating a NHC.