Conducting LB films based on metal complexes of sulphur donor ligands

Preliminary studies are reported on the film forming characteristics of compounds such as dialkyldimethylammonium-M (dmit)₂ and dialkyldimethylammonium-M (mnt)₂ where M = Ni, Pt or Pd. All materials investigated show good monolayer behaviour and deposit readily onto evaporated aluminium or gold films. This is confirmed by surface potential and FTIR measurements. The lateral conductivity of deposited films increases by many orders of magnitude when exposed to bromine vapour.     

Investigations into the response of an optical gas sensor based on polymeric LB films

The response of an NO₂ sensing system based on LB films of a polysiloxane with azobenzene chromophoric side-chains has been investigated. Changes in absorbance on exposure to 100 ppm NO₂ have been recorded using UV-visible absorption spectroscopy from which changes in extinction coefficient (Δ k ≈ 0.033 at 500 nm) have been determined. Shallow angle X-ray reflectivity (SAXR) studies indicate a change in layer thickness from 2.10nm in air to 2.31 nm in 10000 ppm NO₂ together with loss of Bragg detail. Changes in real refractive index (Δn ≈ 0.107 over most of the visible region) for films in air and 100 ppm NO₂ have been deduced from reflectance spectra.     

Precursor method for polymeric LB films

First, the general concept of the “Precursor Method” for the preparation of polymeric Langmuir-Blodgett (LB) films that possess no long alkyl chain between film layers, and the preparation of polybenzothiazole 7 LB film are described. The preparation of 7 LB film was carried out by the same procedure as that used to make polyimide LB films via precursor LB films of polyamides that contain β-carboxyethylthio alkylamine salts 6. Precursor 6 LB film had a Y type structure with monolayer thickness of 2.8 nm, while polybenzothiazole 7 LB film had 0.34 nm. The nonlinear susceptibility χ⁽³⁾ of polybenzothiazole 7 LB film in parallel to the dipping direction was 3.8 × 10⁻¹¹ esu, whereas the susceptibility in the perpendicular direction was about one fifth of that of the parallel direction.     

Gas sensitivity of etioporphyrin metal complexes in thin films

It is shown that porphyrin metal complexes have the potential for the creation of various gas sensors; the gas sensing properties of the materials on their basis change upon the replacement of the central metal atom and substituents in the porphyrin core. Films of etioporphyrin-II were prepared by vacuum deposition onto a front shaft system of electrodes on a pyroceramic support. Calibration dependences of the analytical signal (conductivity) on the concentration of ammonia were obtained. It was found that UV irradiation on the sensor layer enhances the sensitivity of ammonia determination. Relative sensitivities of thin films based on Co(II), Ni(II), Cu(II), Zn(II), Pd(II) and Pt(II) etioporphyrin complexes in the temperature range from 303 K to 423 K and ammonia concentrations from 1.5 to 75 mg/m³ were determined. The relative sensitivity attains a maximum (0.8) at an ammonia concentration of 7.5 mg/m³ for the Co(II) etioporphyrin at 333 K in a dark mode, or at 303 K and under UV irradiation (λ = 406 nm, P = 1 mW). An experimental setup was assembled that allowed measurements at the controlled temperature and humidity of the gas and its mixtures with inert gases or air. The conditions of ammonia detection were optimized.     

Slow relaxation of the magnetization in non-linear optical active layered mixed metal oxalate chains

New Co(II) members of the family of multifunctional materials of general formula [DAMS](4)[M(2)Co(C(2)O(4))(6)]·2DAMBA·2H(2)O (M(III) = Rh, Fe, Cr; DAMBA = para-dimethylaminobenzaldehyde and [DAMS(+)] = trans-4-(4-dimethylaminostyryl)-1-methylpyridinium) have been isolated and characterized. Such new hybrid mixed metal oxalates are isostructural with the previously investigated containing Zn(II), Mn(II), and Ni(II). This allows to preserve the exceptional second harmonic generation (SHG) activity, due to both the large molecular quadratic hyperpolarizability of [DAMS(+)] and the efficiency of the crystalline network which organizes [DAMS(+)] into head-to-tail arranged J-type aggregates, and to further tune the magnetic properties. In particular, the magnetic data of the Rh(III) derivative demonstrate that high spin octacoordinated Co(II) centers behave very similarly to the hexacoordinated Co(II) ones, being dominated by a large orbital contribution. The Cr(III) derivative is characterized by ferromagnetic Cr(III)-Co(II) interactions. Most relevantly, the Fe(III) compound is characterized by a moderate antiferromagnetic interaction between Fe(III) and Co(II), resulting in a ferrimagnetic like structure. Its low temperature dynamic magnetic properties were found to follow a thermally activated behavior (τ(0) = 8.6 × 10(-11) s and ΔE = 21.4 K) and make this a candidate for the second oxalate-based single chain magnet (SCM) reported up to date, a property which in this case is coupled to the second order non linear optical (NLO) ones.     

Theoretical study of mechanisms of non-linear optical response in liquid crystals

Here, we carry out a theoretical analysis of the z scan experiments used to measure the non-linear optical properties of liquid crystals, with the aim of clarifying the mechanism responsible for the observed non-linearity in the nanosecond regime. We consider various orders of non-linear absorption and non-linear refraction in order to illustrate their effects on the resulting z scan curve. The shape of the z scan curve, in principle, contains information about the order of the non-linearity. Qualitative features of the experimental z scan curves are consistent with a fifth order absorption and a third order refraction. However, given the level of disagreement between the calculated and experimental curves, it is not possible to make quantitative statements about the coeffients of the various orders. The magnitude of the refractive part of the non-linearity is consistent with laser heating due to linear absorption. The temporal profile of a two pulse experiment is also consistent with this mechanism. We suggest that the temperature dependence of the non-linear refraction might be explained in terms of a thermal mechanism by accounting for the temperature dependence of the rate of relaxation of the orientational order.     

8-羟基喹啉两亲配合物的LB膜及其电致发光器件研究

制备了两亲配体N-十六烷基-8-羟基-2-喹啉甲酰胺(HL)十个配合物的LB膜。采用π-A等温线和小角X射线衍射等方法研究了这些LB膜的性质和结构。两亲配合物的单分子占有面积为(1.25±0.06)nm^2和(0.75±0.06)nm^2,分别对应于两亲分子中两个喹啉环平躺和环与环之间以一定的角度倾斜于气/水界面。LB膜内分子排列是二维有序的超晶格结构,双层高度(5.0±0.1)nm;LB膜具有导电各向异性,其平面和垂直直流电导率分别为10^-^5S.m^-^1和10^-^9S.m^-^1;LB膜的高荧光性质使之可以用作为电致发光器件的发光材料。以LaL~2(H~2O)~4Cl的LB膜为发光层的单层电致发光器件的驱动电压为9V,发光亮度330cd/m^2,为黄绿色发光。     

The optical rotatory dispersion of transition metal complexes

Using a simple, first order molecular orbital theory the rotatory dispersion is estimated for inorganic complexes which are essentially octahedral. The results restituate the conclusions reached by Moffitt in 1956.     

Monolayer metal coverage of fullerenes: the optical response

A first-principles investigation of the photoabsorption cross section of the specially stable cluster Li₁₂C₆₀ is carried out, including the icosahedral symmetry of the cluster and treating the ions via ab initio pseudopotentials. The role of the coating metal is assessed by computing the same quantity for the fullerene “seed”. It is found that the main absorption features are determined by the carbon molecule, both at low and high excitation energies, in spite of a reduction of 60% for the ionization threshold of Li₁₂C₆₀ as compared to C₆₀. Nonetheless the lithium coating is responsible for small yet clearly observable effects throughout the spectrum, in particular for a more structured and broad strength distribution at excitation energies below the ionization threshold of C₆₀, and a double peak structure in the Mie resonance at ≈20 eV.     

LB膜中NMOB分子构象的研究

利用DFTB3LYP/4-31G^*方法,对2-硝基-5-(N-甲基-N-十八烷基)氨基苯甲酸(NMOB)进行研究。计算结果发现,苯环的5位碳原子、氨基氮原子以及十八烷基链上与其最临近的两个碳原子所组成的两面角(D)约为90ⅲ时,NMOB有最稳构象,在NMOB自交替膜中,NMOB即以这种构象存在;而D=180ⅲ时,体系总能量较最稳构象高出31.57kJ/mol,这种构象存在于NMOB/花生酸镉(CdA)交替膜中,较小的能量差异使NMOB容易在两种构象之间进行转化,在NMOB/花生酸镉(CdA)交替膜中因受到花生酸直立构象紧密排列的诱导作用,NMOB分子以能量相对较高的构象存在。     

两亲性卟啉-紫精化合物LB膜的结构及光电性质研究

本文制备了两亲性卟啉-紫精化合物的LB膜材料, 用π-A等温曲线、吸收光谱、小角和低角X射线衍射以及扫描隧道电镜(STM)等方法研究了LB膜的结构。结果表明, LB膜内分子排列是二维有序的超晶格结构, 卟啉环在基片上的排列呈"站立"状态。单个分子占有面积为1.15nm^2, 单层高度为2.35nm, 相邻裂间的距离为1.07nm。这种规则有序的两亲性卟啉-紫精化合物呈现出良好的光量子收率和光电响应特性。     

Preparation and femtosecond non-linear optical properties of Ag/SiO2 composite thin films

Ag nanoparticles embedded in SiO₂ thin films (Ag/SiO₂ films) were prepared by a multitarget sputtering method. In the optical absorption spectra of the Ag/SiO₂ films, the absorption peak due to the surface plasmon resonance (SPR) of Ag particle was clearly observed at the wavelength of 394–413 nm. The imaginary part of the third-order non-linear susceptibility, Im [χ⁽³⁾], of the Ag/SiO₂ film was estimated to be ?1.1×10^?8 esu measured by the femtosecond Z-scan technique near the SPR peak. The response time of the film measured from the decay of the differential transmission of the pump-probe experiment was 1.3 ps at the SPR peak.     

Isostructural copper-zinc mixed metal complexes for single source deposition of Cu-ZnO composite thin films

The mixed metal complex [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Br]·THF (1) and its isostructural analogues ([Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Cl]·THF (2) and [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Cl/Br]·THF (3)) have been prepared by a simple metal ligand assembly method and were characterized by their melting points, elemental analysis, IR spectroscopy, thermogravimetry and single crystal X-ray structures. The compounds are distinguished only by the nature of the halide ions and are made up of the same [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)X]·THF molecular building block with Cu(3)ZnO(4) cubane moieties as the central core in which the four metal ions and four oxygen atoms are joined together in alternate positions of the cuboid. All the complexes crystallize with similar packing and crystallographically related symmetry settings, distinguished mainly by the degree of disorder within the complexes and the ordering of the complexes in the structures. The triclinic cell of (1) emulates the monoclinic cell of (2) and is pseudomerohedrally twinned by a symmetry operation of the monoclinic cell. The molecules in (2) are 1:1 disordered around a crystallographic mirror plane. The structure of the mixed halogen compound (3) in turn is a superstructure of the less symmetric structures of (1) and (2) formed by ordering of the complexes along the longest axis of (3). Aerosol-assisted chemical vapour deposition (AACVD) experiments showed that they are promising precursors to deposit thin films of crystalline Cu/ZnO composites. The surface morphology, microstructure, chemical composition and crystallinity of the resulting Cu/ZnO composite thin films were analysed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX), which suggest that the films are thin, crystalline, uniform, smooth and tightly adherent to the substrates with average crystallite sizes in a range between 40.2 and 80.0 nm. Particle sizes, shapes and film morphology were investigated as a function of precursor and decomposition temperature.     

Fiber crystal growth from the melt for non-linear optical applications

During several years, we have been involved in the growth and characterization of non-linear optical crystals by the two most common techniques for growing single-crystal fibers from the melt: laser-heated pedestal growth and micro-pulling down. Their specific features are presented in this study and their versatility is demonstrated through two typical examples of incongruently melting materials: K₃Li_2?xNb_5+xO_15+2x (solid solution of the ternary system K₂O–Li₂O–Nb₂O₅) and Ca₅(BO₃)₃F which can only be grown from a flux.     

Photochromic metal complexes: photoregulation of both the nonlinear optical and luminescent properties

A series of dithienylethene (DTE)-containing 2,2'-bipyridine ligands and their zinc(II) diacetate, zinc(II) dichloro, rhenium(I) tricarbonyl bromo, and ruthenium(II) bis(bipyridine) complexes have been designed and synthesized, and their photochromic, photophysical, and quadratic nonlinear optical properties have been studied. Upon UV irradiation at 350 nm, the ligands and complexes undergo ring closure of the DTE units, with a good to excellent photocyclization yield. In the case of the Re(I) and Ru(II) complexes, the photocyclization of the DTE units can also be triggered using visible light, upon excitation into the metal-to-ligand charge-transfer (MLCT) bands at 400 and 490 nm, respectively. Molecular quadratic nonlinear optical (NLO) responses of the complexes have been determined by using either the electrical field induced second harmonic generation (EFISH) or harmonic light scattering (HLS) technique at 1910 nm. These studies reveal a large increase of the second-order NLO activity after UV irradiation and subsequent formation of the ring-closed isomers. This efficient enhancement clearly reflects the delocalization of the π-electron system and the formation of strong push-pull chromophores in the closed forms. The combination of the photochromic DTE-based bipyridine ligand with luminescent Re(I) and Ru(II) fragments also allows the photoregulation of the emission, leading to an efficient quenching of the ligand-based 77 K luminescence and demonstrating that the photocontrol of two optical properties, linear and nonlinear, could be achieved by using the same photochromic ligand.     

Second-order nonlinear optical properties of side-chain liquid crystalline polymers studied by second harmonic generation from thin films

The two independent elements of the second-order nonlinear optical susceptibility tensor of a range of contact poled, donor–acceptor substitued side-chain polymers are reported. The susceptibilities were measured by second harmonic generation from thin films, typically less than 0.5 μm thick, at a fundamental wavelength of 1064 nm. The largest value was χ = 2.64 pm/V which is three times greater than the χ value of KDP and was measured in a nitrobenzylidene side chain, polyhydroxystyrene polymer with an eleven unit alkyl chain spacer attaching the side group to the backbone. Typical susceptibility values obtained were χ～0.3 pm/V and X⁽²⁾₃₃～1 pm/V. The coherence lengths of the materials, which lay in the range 4–12 μm, were measured at 1064 nm by the maker fringe technique using thick, wedge-shaped samples.     

Ceramic films for optical applications

Recent progress is reviewed on the wet chemical synthesis of films for optical applications. Specific attention is directed to planar waveguides and to electrooptic, non-linear optical and electrochromic films, including recent results obtained in our laboratories.