Yanli Chen

High-performance air-stable ambipolar organic field-effect transistor based on tris(phthalocyaninato) europium(III).

A novel sandwich-type tris(phthalocyaninato) europium triple-decker complex bearing peripheral electron-withdrawing groups (see center of figure) is used to fabricate a field-effect transistor by the quasi-Langmuir-Schaefer method. The air-stable, single-component ambipolar OFET device displays the best carrier properties of a device fabricated by solution processing of a single phthalocyanine derivative so far, which makes the complex very promising for applications in nanoelectronics.

Morphology and chirality controlled self-assembled nanostructures of porphyrin–pentapeptide conjugate: effect of the peptide secondary conformation

An optically active porphyrin–pentapeptide conjugate 1, actually a porphyrinato zinc complex covalently linked with a glycinyl–alanyl–glycinyl–alanyl–glycine (GAGAG) peptide chain, was designed and synthesized. The self-assembly properties of this novel porphyrin–pentapeptide conjugate in THF/n-hexane and THF/water were comparatively investigated by electronic absorption, circular dichroism (CD), IR spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) technique. Associated with the different secondary conformation of the pentapeptide chain covalently linked to the porphyrin ring in different solvent systems, self-assembly of conjugate 1 leads to the formation of nanofibers with right-handed helical arrangement and nanotubes with left-handed helical arrangement in a stack of porphyrin chromophores according to the CD spectroscopic result in apolar THF/n-hexane (1u2006:u20063) and polar THF/water (1u2006:u20063) system depending on the cooperation between intramolecular or intermolecular hydrogen bonding interaction with chiral discrimination between pentapeptide chains and porphyrin–porphyrin interactions in the direction parallel to the tetrapyrrole ring of neighboring conjugate molecules. IR spectroscopic result clearly reveals the α-helix and β-sheet secondary conformation, respectively, employed by the pentapeptide chain attached at the porphyrin core in the nanostructures formed in THF/n-hexane (1u2006:u20063) and THF/water (1u2006:u20063). The X-ray diffraction (XRD) result confirms that in the nanotubes, a dimeric supramolecular bilayer structure was formed through an intermolecular hydrogen bonding interaction between two conjugate molecules which, as the building block, self-assembles into the target nanostructures. These results clearly reveal the effect of a secondary conformation of pentapeptide chain in the conjugate molecule on the packing mode of porphyrin chromophore, supramolecular chirality, and morphology of the self-assembled nanostructure. The present result represents not only the first example of organic nanostructures self-assembled from a covalently linked porphyrin–pentapeptide conjugate, but more importantly the first effort towards controlling and tuning the morphology and in particular the supramolecular chirality of porphyrin nanostructures via tuning the secondary conformation of peptides in different solvent systems, which is helpful towards understanding, designing, preparing, and mimicking the structure and role of naturally occurring porphyrin–peptide conjugates. In addition, both nanofibers and nanotubes were revealed to show good semiconducting properties.

The first solution-processable n-type phthalocyaninato copper semiconductor: tuning the semiconducting nature via peripheral electron-withdrawing octyloxycarbonyl substituents

A series of unsymmetrical phthalocyaninato copper complexes simultaneously incorporating electron-withdrawing and electron-donating substituents at the phthalocyanine periphery Cu{Pc(15C5)[(COOC8H17)6]} (2), Cu{Pc[(adj-15C5)2][(COOC8H17)4]} (3), Cu{Pc[(opp-15C5)2][(COOC8H17)4]} (4), Cu{Pc(15C5)3[(COOC8H17)2]} (5) were prepared and isolated. For comparative studies, symmetrical analogues including 2,3,9,10,16,17,24,25-octakis(octyloxycarbonyl)phthalocyaninato copper complex Cu[Pc(COOC8H17)8] (1) and 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninato copper complex Cu[Pc(15C5)4] (6) were also prepared. Their electrochemistry was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). With the help of a solution-based self-assembly process, these compounds were fabricated into organic field effect transistors (OFETs) with top contact configuration on hexamethyldisilazane (HMDS)-treated SiO2/Si substrate. In line with the electrochemical investigation results, a p-type OFET with a carrier mobility (for holes) of 0.06 cm2 V−1 s−1 was shown for Cu[Pc(15C5)4] (6) with electron-donating 15-crown-5 as the sole type of peripheral substituent. In contrast, n-type devices with a carrier mobility (for electrons) of 6.7 × 10−6–1.6 × 10−4 cm2 V−1 s−1 were achieved for 1–5 with electron-withdrawing octyloxycarbonyl substituents at the peripheral positions of phthalocyanine ring, indicating the significant effect of electron-withdrawing octyloxycarbonyl substituents on tuning the nature of phthalocyanine organic semiconductors. The present results represent the first example of solution-processed n-type phthalocyanine-based OFET devices.

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.

Morphology controlled nano-structures of an octa(phenoxy)-substituted phthalocyaninato zinc complex: solvent effect on the self-assembly behaviour

The 2,3,9,10,16,17,24,25-octakis(phenoxy)phthalocyaninato zinc, (Zn[Pc(OPh)8]) was fabricated into nano-/micro-structures via solution-phase self-assembly. The self-assembling properties of Zn[Pc(OPh)8] in coordinating and non-coordinating solvents (methanol and n-hexane) have been comparatively studied by electronic absorption, fluorescence, Fourier transform infrared spectroscopy (FT-IR), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. The conducting properties were evaluated by current–voltage (I–V) measurements. Due mainly to the presence of different intermolecular Zn–O coordination interactions between the Zn[Pc(OPh)8] molecules in n-hexane and between the Zn[Pc(OPh)8] and solvent molecules in methanol, the self-assembly of the Zn[Pc(OPh)8] results in nano-/micro-structures with distinctly different morphology as follows: nanobelts in n-hexane, and soft nano-sticks, microscale needle mushroom as well as pine leaves in methanol depending on aggregation time. The size and/or morphological evolution of the nanostructures have been clearly revealed during the self-assembly process. The present result appears to represent the first effort toward realization of controlling and tuning the biomorphs of self-assembled nanostructures of phthalocyanine-related complexes through the solvent coordinating effect. Furthermore, both nanobelts and micrometer-sized pine leaves were revealed to show good semiconductor features.

5,10,15,20-tetra(4-pyridyl)porphyrinato zinc coordination polymeric particles with different shapes and luminescent properties

Micro-scale three-dimensional coordination polymer particles (CPPs) have been synthesized from the surfactant-assisted reaction of Zn(OAc)2·2H2O and 5,10,15,20-tetra(4-pyridyl)porphyrin (H2TPyP) in DMF. The three-dimensional (3D) micro-prisms and micro-octahedra of the CPPs were obtained at different temperatures as found by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and a statistical analysis of the size distribution results. X-Ray diffraction (XRD) analysis revealed a circular hexametric cage structure cross-linked by a Zn–N axial coordination of the pyridyl ligands inside the micro-scale CPPs. Further support for this coordination polymerization mode of the micro-CPPs came from IR spectroscopy. The UV–vis spectra clearly show the formation of J-type aggregates in both the microstructures. The micro-CPPs show a stronger luminescence intensity over the individual porphyrin molecules, which is presumably due to the high surface area of the ZnTPyP-CPPs. Nevertheless, nitrogen adsorption/desorption isotherm measurements were performed to confirm the larger surface area and increased porosity of the micro-prisms and micro-octahedra relative to the self-assembled micro-rods of ZnTPyP, indicating the potential application of the two CPPs microstructures in the field of gas adsorption. The surfactant-assisted synthetic route appears to provide a promising method for the construction of highly organized three-dimensional organic micro-structures of 5,10,15,20-tetra(4-pyridyl)porphyrin derivatives.

Controlled preparation of CdS nanoparticle arrays in amphiphilic perylene tetracarboxylic diimides: organization, electron-transfer and semiconducting properties

Langmuir monolayers of two amphiphilic perylene tetracarboxylic diimide (PDI) derivatives, PDI-1 and PDI-2, which are modified with different numbers of hydrophilic polyoxyethylene/hydrophobic alkoxy side-chains, have been used as not only organic templates but also good functional organic materials to produce the first examples of rose- and petal-like nano-particle arrays of cadmium sulfide (CdS)–PDI composites with a controllable and tunable size (from 40, 60 to 80 nm for nano-roses; from 20 to 30 nm for nano-petals), respectively. These newly fabricated CdS–PDI hybrid nanostructures were comparatively studied using a wide range of methods including SEM, TEM, electronic absorption, fluorescence emission and X-ray diffraction analysis. The crystalline regions for CdS were identified to be hexagonal wurtzite with (101) and (001) face preferred growth on the PDI-1 and PDI-2 monolayers, respectively, associated with the polyoxyethylene side chains architecture changing from parallel to the subphase surface for PDI-1 to perpendicular to the subphase surface for PDI-2. Furthermore, electron-transfer from PDI molecules to CdS nanocrystals is established by both quenching the photoluminescence intensity and changing the lifetime of photoluminescence emission of PDI in the hybrid nanoparticle arrays. In particular, a significantly enhanced conductivity for both nano-roses and nano-petals of CdS–PDI nanocomposites was achieved, relative to that of the individual component, due to the existence of the densely packed molecular architecture in the film matrix and the large interfacial area between the two components that removed the charge transporting bottleneck by creating an interpenetrating network of the hybrid materials, implying the potential of providing synergetic semiconducting properties of the present hybrid organic–inorganic nanomaterials.

Synthesis, self-assembly, and semiconducting properties of phenanthroline-fused phthalocyanine derivatives

Two novel unsymmetrical phenanthroline-fused phthalocyanine derivatives, namely metal free 2,3,9,10,16,17-hexakis(n-butyloxy)-22,25-diaza(1,10-phenanthrolino)[5,6-c1]phthalocyanine H2[Pc(OC4H9)6(dicqn)] (1) and its zinc complex Zn[Pc(OC4H9)6(dicqn)] (2), were designed, synthesized, and characterized by a series of spectroscopic methods in addition to elemental analysis. Their self-assembly properties in CHCl3–methanol were comparatively investigated by electronic absorption spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques. Effective intermolecular π–π interactions between metal free phenanthroline-fused phthalocyanine molecules in a face-to-face manner led to the formation of nanowires in CHCl3–methanol, whereas the phenanthroline-fused phthalocyaninato zinc complex self-assembles into ribbonlike nanobundles with a head-to-tail arrangement depending mainly on Zn–N coordination bonding with a slipped π-stacking interaction between neighboring phthalocyanine molecules. Nevertheless, the aggregates formed from both compounds, in particular the metal free one, were revealed to show good semiconducting properties with a conductivity as high as 1.0 × 10−4 S cm−1.

Effects of metal–ligand coordination on the self-assembly behaviour of a crown ether functionalised perylenetetracarboxylic diimide

A novel perylenetetracarboxylic diimide (PDI) derivative, N,N′-di(4′-benzo-15-crown-5-ether)-1,7-di(4-tert-butyl-phenoxy)perylene-3,4;9,10-tetracarboxylic diimide (CRPDI), has been synthesised and characterised. Dimerisation of CRPDI is induced by the presence of K+ in CHCl3 or spontaneously occurs in methanol, as revealed by absorption and emission spectroscopy. In particular, the formation of co-facial dimer in the presence of K+ proceeds in a three-stage process, as indicated by absorption spectroscopy. The belt- and rope-like nanostructures of CRPDI fabricated from methanol and CHCl3 solution in the presence of K+ are obtained by scanning electron microscopy. Furthermore, the conductivity of the rope-like nanostructures from the cation-induced dimeric species is more than ca. 1 order of magnitude higher than the belt-like nanostructures from the solvent-induced dimeric species. The present result represents the further effort towards realisation of controlling and tuning the morphology of self-assembled nanostructures of PDI derivatives through molecular design and synthesis. It will be valuable for the design and preparation of PDI-based nano-(opto)electronic devices with good performance due to the close relationship between the molecular ordering and dimensions of nanostructures and the performance of nanodevices.

Self-Assembled Organic–Inorganic Hybrid Nanocomposite of a Porphyrin Derivative and CdS

A porphyrin derivative, 5-(4-carboxylphenyl)-10,15,20-tris(4-chlorophenyl) porphyrin (PorCOOH), was synthesized and self-assembled as a monolayer thin solid film on the modified surface of a quartz substrate by an ester bond between –COOH groups of PorCOOH molecules and –OH groups of the hydrophilic pretreated SiO2 surface. An analysis of the spectral change revealed the J-aggregate nature of PorCOOH molecules in the obtained thin solid film. With this thin solid film of PorCOOH as a template, CdS nanoparticles were deposited on it in situ, which were further characterized by electronic absorption, fluorescence, and energy-dispersive X-ray spectroscopy. The morphology of CdS nanoparticles is disklike, and the diameter is ca. 40–60xa0nm, determined by scanning electronic microscopy. Furthermore, electron transfer between the organic layer and CdS nanoparticles was deduced through fluorescence quenching and theoretical analysis.