Guifen Lu

Morphology controlled self-assembled nanostructures of sandwich mixed (phthalocyaninato)(porphyrinato) europium triple-deckers. Effect of hydrogen bonding on tuning the intermolecular interaction.

A series of five novel sandwich-type mixed (phthalocyaninato)(porphyrinato) europium triple-decker complexes with different numbers of hydroxyl groups at the meso-substituted phenyl groups of porphyrin ligand 1-5 have been designed, synthesized, and characterized. Their self-assembly properties, in particular the effects of the number and positions of hydroxyl groups on the morphology of self-assembled nanostructures of these triple-decker complexes, have been comparatively and systematically studied. Competition and cooperation between the intermolecular pi-pi interaction and hydrogen bonding in the direction perpendicular to the pi-pi interaction direction for different compounds were revealed to result in nanostructures with a different morphology from nanoleafs for 1, nanoribbons for 2, nanosheets for 3, and curved nanosheets for 4 and to spherical shapes for 5. The IR and X-ray diffraction (XRD) results reveal that, in the nanostructures of triple-decker 2 as well as 3-5, a dimeric supramolecular structure was formed through an intermolecular hydrogen bond between two triple-decker molecules, which as the building block self-assembles into the target nanostructures. Electronic absorption spectroscopic results on the self-assembled nanostructures reveal the H-aggregate nature in the nanoleafs and nanoribbons formed from triple-deckers 1 and 2 due to the dominant pi-pi intermolecular interaction between triple-decker molecules, but the J-aggregate nature in the curved nanosheets and spherical shapes of 4 and 5 depending on the dominant hydrogen bonding interaction in cooperation with pi-pi interaction among the triple-decker molecules. Electronic absorption and XRD investigation clearly reveal the decrease in the pi-pi interaction and increase in the hydrogen bonding interaction among triple-decker molecules in the nanostructures along with the increase of hydroxyl number in the order of 1-5. The present result appears to represent the first effort toward realization of controlling and tuning the morphology of self-assembled nanostructures of sandwich tetrapyrrole rare earth complexes through molecular design and synthesis.

Tuning the morphology of self-assembled nanostructures of amphiphilic tetra(p-hydroxyphenyl)porphyrins with hydrogen bonding and metal–ligand coordination bonding

Typical amphiphilic metal-free tetrakis(4-hydroxyphenyl)porphyrin H2THPP (1) and tetrakis(4-hydroxyphenyl)porphyrinato copper complex CuTHPP (2) were fabricated into organic nanostructures by a phase-transfer method. Their self-assembly properties in aqueous solution have been comparatively studied with those of tetra(phenyl)porphyrin H2TPP (3) by electronic absorption and Fourier transform infrared (FT-IR) spectroscopy, transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), and X-ray diffraction (XRD) techniques. Experimental results reveal different molecular packing models in these aggregates, which in turn result in self-assembled nanostructures with different morphologies from nano-scale hollow spheres for 1, nanoribbons for 2, to nanobelts for 3. The present study, representing part of our continuous efforts towards understanding the relationship between synergistic interplay among noncovalent interactions such as the π–π interaction, metal–ligand coordination bonding, and hydrogen bonding in controlling and tuning the morphology of self-assembled nanostructures of tetrapyrrole derivatives, will provide information helpful for preparing self-assembled nanostructures with controlled molecular packing conformations and morphologies through molecular modification.

Molecular oxygen reduction electrocatalyzed by meso-substituted cobalt corroles coated on edge-plane pyrolytic graphite electrodes in acidic media.

Five meso-substituted cobalt(III) corroles were examined as to their catalytic activity for the electoreduction of O(2) when coated on an edge-plane pyrolytic graphite electrode in 1.0 M HClO(4). The investigated compounds are represented as (TpRPCor)Co(PPh(3)), where TpRPCor is the trianion of a para-substituted triphenylcorrole and R = OMe, Me, H, F, or Cl. Three electrochemical techniques, cyclic voltammetry, linear sweep voltammetry with a rotating disk electrode (RDE), and voltammetry at a rotating ring disk electrode (RRDE), were utilized to evaluate the catalytic activity of the corroles in the reduction of O(2). Cobalt corroles containing electron-withdrawing substituents were shown to be better catalysts than those having electron-donating groups on the three meso-phenyl rings of the triarylcorroles.

Tuning the semiconducting nature of bis(phthalocyaninato) holmium complexes via peripheral substituents

The semiconducting properties of the heteroleptic and homoleptic bis(phthalocyaninato) holmium complexes bearing electron-withdrawing phenoxy substituents at the phthalocyanine periphery, namely Ho(Pc)[Pc(OPh)8] (1) and Ho[Pc(OPh)8]2 (2) [Pc = unsubstituted phthalocyaninate; Pc(OPh)8 = 2,3,9,10,16,17,23,24-octaphenoxyphthalocyaninate] have been investigated comparatively. Using a solution-based Quasi–Langmuir–Shafer (QLS) method, the thin solid films of the two compounds were fabricated. The structure and properties of the thin films were investigated by UV-vis absorption spectra, X-ray diffraction (XRD) and atomic force microscopy (AFM). Experimental results indicated that H-type molecular stacking mode with the common preferential molecular “edge-on” orientation relative to the substrate has been formed, and the intermolecular face-to-face π–π interaction and film microstructures are effectively improve by increasing the number of phenoxy substituents of the Pc periphery within the double-decker complexes. The electrical conductivity of Ho(Pc)[Pc(OPh)8] films was measured to be approximately 4 orders of magnitude larger than that of Ho[Pc(OPh)8]2 films, indicating significant effect of peripheral electron-withdrawing phenoxy groups on conducting behaviour of bis(phthalocyaninato) holmium complexes. In addition, the gas sensing behaviour of the QLS films of 1 and 2 toward electron donating gas, NH3, was investigated in the concentration range of 15–800 ppm. Surprisingly, contrary responses towards NH3 were found for the QLS films of 1 and 2. In the presence of NH3, the conductivity of the films of Ho(Pc)[Pc(OPh)8] (1) decreased while the conductivity of the films of Ho[Pc(OPh)8]2 (2) increased. This observation clearly demonstrated the p- and n-type semiconducting nature for 1 and 2, respectively. Furthermore, compared to the heteroleptic 1 having a hole mobility of 1.7 × 10−4 cm2 V−1 s−1, homoleptic 2 exhibits an electron mobility as high as 0.54 cm2 V−1 s−1. Therefore, the inversion of the semiconducting nature of the double-deckers from p- to n-type can be successfully and easily realized just by increasing the number of peripheral phenoxy groups attached to the conjugated Pc cores.

Photochromic nanostructures based on diarylethenes with perylene diimide.

A bisthienylethene-functionalized perylene diimide (BTE-PDI) photochromic dyad was synthesized for self-assembly into 1-D nanotubes by a reprecipitation method. SEM and TEM observations showed that the nanotubes were formed from their 0-D precursors of hollow nanospheres. HR-TEM images revealed that both the nanospheres and the nanotubes have highly ordered lamellar structure, indicating the hierarchical process during assembly. The IR and XRD results revealed that DAE-PDI molecules were connected through intermolecular hydrogen bonds to form building blocks that self-assembled into nanostructures. Electronic absorption and fluorescence spectroscopic results indicated the H-aggregate nature of the self-assembled nanostructures. Competition and cooperation between the dipole-dipole interaction, intermolecular pi-pi stacking, and hydrophilic/hydrophobic interaction are suggested to result in nanostructures. Reconstruction was found to happen during the morphology transition progress from the 0-D nanospheres to the 1-D nanotubes, which was driven by donor-acceptor dipole-dipole interactions. Green emission at 520 nm originating from the DAE subunit was observed for the aggregates of vesicles and nanotubes, which could be regulated by photoirradiation with 365 nm light, suggesting the nanoaggregates to be photochromic switches.

β-Nitro-substituted free-base, iron(III) and manganese(III) tetraarylporphyrins: synthesis, electrochemistry and effect of the NO2 substituent on spectra and redox potentials in non-aqueous media

Two free-base and four metal derivatives of substituted tetraarylporphyrins containing a nitro-substituent on the β-pyrrole position of the macrocycle were synthesized and characterized by UV-vis, FTIR, 1H NMR and mass spectrometry as well as electrochemistry and spectroelectrochemistry in non-aqueous media. The porphyrins are represented as (NO2TmPP)M and (NO2TdmPP)M, where M = 2H, FeIIICl or MnIIICl, m is a CH3 group on the para-position of the four meso-phenyl rings of the tetraphenylporphyrin (TPP) and dm represents two OCH3 substituents on the meta-positions of each phenyl ring of the TPP macrocycle. UV-visible spectra of the nitro-substituted porphyrins exhibit absorption bands which are red-shifted by 4–11 nm as compared to bands of the same substituted tetraarylporphyrins lacking a nitro substituent. Three or four reductions are observed for each iron and manganese nitroporphyrin, the first of which is metal-centered, leading to formation of an Fe(II) or Mn(II) complex. Further reduction at the metal center occurs for the iron porphyrins but this reaction proceeds via an Fe(II) π anion radical in the case of the two nitro-substituented derivatives. The β-nitro-substituted porphyrins are easier to reduce and harder to oxidize than the corresponding compounds lacking a nitro group. The effect of NO2 substituent on reduction/oxidation potentials and the site of electron transfer was also discussed.

Synthesis, characterization and solvent/structural effects on spectral and redox properties of cobalt triphenylcorroles in nonaqueous media

Five cobalt(III) triphenylcorroles with different electron-withdrawing or electrondonating substituents and an axially bound triphenylphosphine ligand were synthesized and characterized by spectroscopic and electrochemical techniques. The investigated compounds are represented as (4-XPh)3CorCo(PPh3), where Ph3Cor is the trianion of a triphenylcorrole and X is a OMe, Me, H, F or Cl substituent on the meso-phenyl rings. Each corrole was examined by UV-vis, 1H NMR and IR spectroscopy, mass spectrometry, electrochemistry and thin-layer spectroelectrochemistry. Redox potentials and spectra of each oxidized and reduced species were examined in dichloromethane and N,N′-dimethylformamide containing 0.1 M tetra-n-butylammonium perchlorate. Each Co(III) corrole undergoes up to five one-electron transfer reactions, some of which are reversible and others which are not. The CoIII/CoII process is irreversible in both solvents due to the loss of the triphenylphosphine axial ligand following electron transfer. The CoII/CoI process is reversible in DMF but irreversible in CH2Cl2 due to a homogenous chemical reaction between the electrogenerated Co(I) corrole and the chlorinated solvent. The potential for the first oxidation of the investigated corroles varies little with change of solvent, consistent with the lack of solvent binding to the neutral and singly oxidized forms of (4-XPh)3CorCo(PPh3). However, a single DMF molecule strongly binds to the doubly oxidized corrole in DMF or DMF/CH2Cl2 mixtures. This results in an easier oxidation and a negative shift of ~200 mV in E1/2 upon going from CH2Cl2 to DMF as solvent. The effect of substitutents and solvent on redox potentials is discussed and an overall electroreduction/electrooxidation mechanism is proposed

Reductive dechlorination of DDT electrocatalyzed by synthetic cobalt porphyrins in N,N′-dimethylformamide

Two cobalt porphyrins, (OEP)CoII and (TPP)CoII, where OEP and TPP are the dianions of octaethylporphyrin and tetraphenylporphyrin, respectively, were examined as electrocatalysts for the reductive dechlorination of DDT (1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane) in N,N′-dimethylformamide (DMF) containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). No reaction is observed between DDT and the porphyrin in its Co(II) oxidation state but this is not the case for the reduced Co(I) forms of the porphyrins which electrocatalyze the dechlorination of DDT, giving initially DDD (1,1-bis(4-chlorophenyl)-2,2-dichloroethane), DDE (1,1-bis(4-chlorophenyl)-2, 2-dichloroethylene) and DDMU (1,1-bis(4-chlorophenyl)-2-chloroethylene) as determined by GC-MS analysis of the reaction products. A further dechlorination product, DDOH (2,2-bis(4-chlorophenyl)ethanol), is also formed on longer timescales when using (TPP)Co as the electroreduction catalyst. The effect of porphyrin structure and reaction time on the dechlorination products was examined by GC-MS, cyclic voltammetry, controlled potential electrolysis and UV-visible spectroelectrochemistry and a mechanism for the reductive dechlorination is proposed.

Synthesis and electrochemical properties of meso-phenyl substituted copper corroles: Solvent effect on copper oxidation state

Two meso-phenyl chloro-substituted copper corroles were synthesized and characterized by a variety of spectroscopic techniques. The investigated compounds are represented as ((ClPh)3Cor)Cu and ((Cl2Ph)3Cor)Cu, where (ClPh)3Cor and (Cl2Ph)3Cor are the trianions of the 5,10,15-tri- (4-chlorophenyl)corrole and 5,10,15-tri(2,4-dichlorophenyl)corrole, respectively. UV-visible and ESR spectroscopy revealed that the electronic ground state of each copper corrole is solvent dependent. Both compounds contain Cu(III) corroles in the solid state and in solutions of CH2Cl2, but an equilibrium exists between Cu(III) and its Cu(II) form in pyridine, DMSO or DMF. The Cu(II) corrole could also be generated by controlled potential reduction in a thin-layer cell, which is reversible in CH2Cl2 or DMF containing 0.1 M TBAP. The structure of ((ClPh)3Cor)Cu was determined by a single-crystal X-ray study.

Synthesis and Characterization of Rare Earth Corrole-Phthalocyanine Heteroleptic Triple-Decker Complexes.

We recently reported the first example of a europium triple-decker tetrapyrrole with mixed corrole and phthalocyanine macrocycles and have now extended the synthetic method to prepare a series of rare earth corrole-phthalocyanine heteroleptic triple-decker complexes, which are characterized by spectroscopic and electrochemical methods. The examined complexes are represented as M2[Pc(OC4H9)8]2[Cor(ClPh)3], where Pc = phthalocyanine, Cor = corrole, and M is Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), or Tb(III). The Y(III) derivative with OC4H9 Pc substituents was obtained in too low a yield to characterize, but for the purpose of comparison, Y2[Pc(OC5H11)8]2[Cor(ClPh)3] was synthesized and characterized in a similar manner. The molecular structure of Eu2[Pc(OC4H9)8]2[Cor(ClPh)3] was determined by single-crystal X-ray diffraction and showed the corrole to be the central macrocycle of the triple-decker unit with a phthalocyanine on each end. Each triple-decker complex undergoes up to eight reversible or quasireversible one-electron oxidations and reductions with E1/2 values being linearly related to the ionic radius of the central ions. The energy (E) of the main Q-band is also linearly related to the radius of the metal. Comparisons are made between the physicochemical properties of the newly synthesized mixed corrole-phthalocyanine complexes and previously characterized double- and triple-decker derivatives with phthalocyanine and/or porphyrin macrocycles.