Xu-Sheng Feng

Influence of ligands on the photoluminescent properties of Eu3+ in europium β-diketonate/PMMA-doped systems

Abstract Three kinds of europium β-diketonates Eu(DBM) 3 , Eu(BA) 3 and Eu(TTA) 3 (DBM: Dibenzoylmethane; BA: 1-Benzoylacetone; TTA: Thenoyltrifluoroacetone) were doped in poly(methyl methacrylate) (PMMA) matrix. The doped systems were studied by using photoluminescent (PL) spectroscopy, emission decay experiments and X-ray diffractometry. Eu(III) ions in the doped Eu(DBM) 3 /PMMA systems have two distinct symmetric sites and the emission band changes greatly with the compositions. Eu(III) in the Eu(BA) 3 /PMMA systems gives only one symmetric site in the doped systems and the emission band changes slightly with the compositions. Although two distinct symmetric sites of Eu(III) can be distinguished in the doped systems of Eu(TTA) 3 /PMMA, the two sites have similar 5 D 0 lifetimes and the luminescent spectra almost do not change with the compositions. XRD reveals that crystallites were formed in the doped Eu(DBM) 3 /PMMA systems that have different crystalline structure from that of the chelate, and Eu(BA) 3 and Eu(TTA) 3 exist in amorphous state in the doped systems. The difference between the PL properties and structures of the doped systems for the three kinds of chelates should be attributed to different interactions between the chelate molecules and between the chelate and PMMA.

Influences of hydrophilic and hydrophobic substituents on the organization of supramolecular assemblies of porphyrin derivatives formed at the air/water interface

Abstract Monolayers and Langmuir–Blodgett (LB) films of several kinds of porphyrin derivatives that have different substituted alkyl chain length, chain numbers and central metals were studied by π-A isotherms, UV–Vis, polarized UV–Vis and fluorescence spectroscopy and low angle X-ray diffractometry (LAXD). The orientation angles of porphyrin rings and alkyl chains were derived from the polarized UV–Vis spectra and LAXD patterns of the monolayers or LB films, respectively. The rings of the freebase porphyrins with different alkyl chain length or number have similar orientation angles in the films due to the same hydrophilic groups on the rings, and those of metal porphyrins have different orientation angles from each other. The orientation of the alkyl chains is related to the special positions of the chains on the rings and the orientation of the rings. The influences of the hydrophilicity of the hydrophilic groups and the alkyl chain number and length on the organization of the supramolecular assemblies of the porphyrin derivatives were discussed.

Central metal effect on the organization of porphyrin LB films

Monolayers and Langmuir–Blodgett (LB) films of 5,10,15,20-tetra-4-oxy (2-stearic acid) phenylporphyrin (TSPP) and its complexes TSPPCu(II) and TSPPMn(III)Cl have been studied. π–A isotherms show that the molecular areas of the three molecules are similar to one another, while the polarized UV-vis spectra of the transferred films show different tilt angles of macrocycles with respect to the substrates: TSPP, 31°; TSPPCu(II), 0°; TSPPMn(III)Cl, 52°. The UV-vis spectra show that the π–π interactions between porphyrin macrocycles in monolayers of these three porphyrins are different. The Brewster angle microscopy (BAM) observations suggest that the monolayer behavior is also dependent on the central metal ions. These results indicate that the central metal ions have great influence on the organization of the films.

Supramolecular assemblies of Eu(TPyP)Pc at the air/water and air/Cd2+ aqueous solution interfaces

Abstract The supramolecular assemblies of sandwich-type complex Eu(TPyP)Pc (TPyP: tetrapyridylporphyrin; Pc: phthalocyanine) were fabricated at the air/water and air/Cd2+ aqueous solution interfaces. One-dimensional columns and two-dimensional coordinate framework were formed, respectively, and characterized by surface pressure–area (π–A) isotherms, UV–vis spectra and polarized UV–vis spectra. The orientation angle of macrocycles with respect to the substrate surface is about 38° and 32° for the Langmuir–Blodgett films from pure water and Cd2+ subphase surfaces, respectively.

Synthesis and monolayer formation of liquid crystal polysiloxanes having a lateral side chain with a perfluoroalkyl chain

Abstract Liquid crystal polysiloxanes with a lateral 4-(4-cyanophenoxycarbonyl)phenyl 4-(2-perfluoroalkylethoxy)-2-propyleneoxybenzoate side group and a 4-decyloxy-2-propyleneoxy-benzoate hydrocarbon analogue were prepared, and the mesomorphic properties were determined by the microscopic observation and differential scanning calorimeter (DSC) thermogram, and the layer structure of the smectic A phase was characterized by an X-ray diffraction experiment. The introduction of the perfluoroalkyl chain to the polymer remarkably enhances the smectic properties due to the strong fluorophilic interactions around the perfluoroalkyl chain. The effect of the perfluoroalkyl chain on the monolayer formation was studied at the air–water interface. The surface pressure–area isotherms show that the perfluoroalkyl chain enhances the stability of the monolayer versus surface pressure. In the condensed state the cyano group in the side chain is assumed to be anchored on the water surface and the mean axis of the liquid crystal core is approximately normal to the water surface. The monolayers were easily deposited on a hydrophobic glass slide, giving uniform Langmuir–Blodgett (LB) films by the vertical deposition method. The X-ray diffraction results indicate that the perfluorooctyl chain effectively stabilizes the layer structure in the multilayer LB film at room temperature. The side chain monomers also show a similar behavior to the polymers and give uniform LB films on hydrophobic glass slides.

Influence of molecular structures of europium bisphthalocyanines on organization of supramolecular assemblies formed at the air/water interface

Abstract The monolayers at the air/water interface, the Langmuir-Blodgett (LB) monolayers and multilayers on solid substrates of five kinds of europium bisphthalocyanines EuPc 2 (Eu1), EuPc[Pc(OC 5 H 11 ) 8 )] (Eu2), EuPc[Pc(C 7 H 15 ) 8 ] (Eu3), Eu[Pc(OC 5 H 11 ) 8 )] 2 (Eu4) and Eu[Pc(C 7 H 15 ) 8 ] 2 (Eu5) were characterized by using π – A isotherms, UV-vis spectra, polarized UV-vis spectra, low-angle X-ray diffraction (LAXD) and transmission electron microscopy (TEM). The results demonstrate that the different molecular structures have great influence on the orientation of the macrocycles, on the configuration of the molecules and on the organization of the supramolecular assemblies at the air/water interface. In the aggregates of Eu1 molecules, the macrocycles stack closely in a face-to-face mode with an orientation angle of 51°. Eu2 and Eu4 form homogeneous monolayers at a lower surface pressure due to the stronger hydrophilicity of the substituents, in which the molecules take the face-on configuration with the Pc rings in contact with the water surface. The orientation angles are ca. 45° and 30°, respectively, and the chains extend to the air. Eu5 molecules take an edge-on configuration with the ring orientation angle of ca. 30° at the air/water interface form rod-like supramolecular structures. Eu3 does not form an ordered structure at the air/water interface due to the asymmetric molecular structure.

Study of the photophysical properties of composite film assembled of porphyrin and TiO2 nanoparticles

Abstract In this paper, the formation, structure, and photophysical properties of functional mixed film of 5,10,15,20-tetra-4-(2-decanoic acid)phenyl porphyrin (TDPP) with TiO2 nanoparticles formed from the 2D sol-gel process of tetrabutoxyltitanium (TBT) at the air/water interface is reported. The composite multilayer films were assembled by transferring the mixed monolayer onto quartz plates. The diameter distribution and crystallinity of TiO2 particles were estimated by TEM observation and electron diffraction. The sensitization of TDPP upon TiO2 nanoparticles was confirmed by the spectral changes of UV–visible absorption and fluorescence of TDPP in the composite films. Furthermore the photosensitization greatly affected the photocatalytic activity of TiO2 particles with respect to the degradation of methylene blue (MO).

Europium complex nanoparticles: preparation, characterization and optical properties

Spherical, rod-like europium complex nanocrystals or their irregular ultrafine particles have been synthesized in a colloidal solution by using cationic surfactant as a soft template. These Eu complex nanoparticles showed much stronger fluorescence emission than a precipitate prepared from the same solutions but without surfactant.

The properties and structural characteristics of Langmuir-Blodgett films of two metalloporphyrin complexes with differential substituents☆

The LB films of two metalloporphyrin complexes with different substituents (NiTPP(OH), Cu11TPP(COOH)) have been investigated. The π-A isotherms are given. The composition and structure of the films were identified by XPS, UV-visible spectra, SEM, polarized absorption and X-ray diffraction. Interaction between molecules in the films of NiTPP(OH) was evident from the red shift in the visible spectroscopy, while that of Cu11TPP (COOP) was not. The porphyrin ring of the NiTPP (OH) molecule was tilted on the subphase surface and transferred onto substrates in a similar orientation, but that of Cu11-TPP(COOH) was parallel to the film plane. The electric resistance of NiTPP(OH) films was less than that of Cu11TPP(COOH) by ten orders of magnitude.

Monolayer and multilayer of a liquid crystal copolysiloxane at the air–water interface

Abstract This paper describes the phase transition behavior of a copolysiloxane ( 1 ) bearing a 4-cyanophenyl benzoate core at the terminal of the side chain. While polymer 1 exhibits only a nematic phase in bulk, it easily forms layer structures involving monolayer, trilayer, and complex multilayers at the air–water interface. In the monolayer state the cyano groups are anchored on the water surface and the aromatic moieties involving the copolysiloxane chain are directed towards the air phase. The trilayer has a partially bilayer structure on the top of the monolayer, where the layer structure was confirmed by X-ray diffraction measurement of the LB films, giving the layer spacing of 1.47 times of the calculated side chain length. Complex multilayer transitions were also observed by a further compression or changing subphase temperature.