The trans-Bis(p-thioetherphenylacetynyl)bis(phosphine)platinum(II) Ligands: A Step towards Predictability and Crystal Design

Two organometallic ligands L1 (trans-[p-MeSC₆H₄C≡C-Pt(PR₃)₂-C≡CC₆H₄SMe; R = Me]) and L2 (R = Et) react with CuX salts (X = Cl, Br, I) in MeCN to form one-dimensional (1D) or two-dimensional (2D) coordination polymers (CPs). The clusters formed with copper halide can either be step cubane Cu₄I₄, rhomboids Cu₂X₂, or simply CuI. The formed CPs with L1, which is less sterically demanding than L2, exhibit a crystallization solvent molecule (MeCN), whereas those formed with L2 do not incorporate MeCN molecules in the lattice. These CPs were characterized by X-ray crystallography, thermogravimetric analysis, IR, Raman, absorption, and emission spectra as well as photophysical measurements in the presence and absence of crystallization MeCN molecules for those CPs with the solvent in the lattice (i.e., [(Cu₄I₄)L1·MeCN] _n (CP1), [(Cu₂Br₂)L1·2MeCN] _n (CP3), and [(Cu₂Cl₂)L1·MeCN] _n (CP5)). The crystallization molecules were removed under vacuum to evaluate the porosity of the materials by Brunauer-Emmett-Teller (N₂ at 77 K). The 2D CP shows a reversible type 1 adsorption isotherm for both CO₂ and N₂, indicative of microporosity, whereas the 1D CPs do not capture more solvent molecules or CO₂.

Insights into the effect of ketylimine, aldimine, and vinylene group attachment and regiosubstitution on the fluorescence deactivation of fluorene

The spectroscopic and electrochemical properties of a 9-substituted fluorene ketylimine (3) were investigated and compared with those of its vinylene analogue (4) to determine the origins of the quenched fluorescence of these compounds. The predominate mode of singlet excited state deactivation of the heteroatomic fluorene was found to be internal conversion involving bond rotation. Meanwhile, its carbon counterpart was found to undergo deactivation preferentially by intersystem crossing to form its triplet, which was confirmed by laser flash photolysis. Both 3 and 4 quenched the fluorescence of fluorene with diffusion-controlled rate constants, implying that the singlet excited states of 3 and 4 are also quenched by intramolecular photoinduced electron transfer (PET). This deactivation mode was found to be exergonically favorable (–90 kJ/mol for 3 and –81 kJ/mol for 4) according to the Rehm–Weller equation. The position of the heteroatomic bond on the fluorene moiety was further found to influence the singlet excited state deactivation pathway. The 2-substituted regioisomer decayed predominately by intramolecular PET and its fluorescence can be restored by acid protonation. Conversely, the PET mechanism is a minor deactivation mode for the 9-substituted fluorene derivative and its fluorescence can be enhanced by suppressing bond rotational modes, possible at low temperature and potentially in thin films.

Recent Progress on the Photonic Properties of Conjugated Organometallic Polymers Built Upon the trans-Bis(para-ethynylbenzene)bis(phosphine)platinum(II) Chromophore and Related Derivatives

This review article surveys the electronic and photophysical properties of conjugated organometallic polymers built upon the title compound and its related derivatives focussing primarily on systems investigated in our laboratories. The general structure of the polymers is (trans-bis(para-ethynylbenzene)bis(phosphine)platinum(II)-G)(n) where G is a conjugated group such as thiophene, fluorene, carbazole, substituted silole, quinone derivative, and metalloporphyrin residue, or a non-conjugated main-group moiety. Systems based on substituted phenylene units and other related fused rings are also discussed. The phosphine ligands are generally triethyl- or tri-n-butylphosphine groups. These trans-platinum(II) polymers and the corresponding model compounds are compared to the corresponding ortho-derivatives in the quinone series, and the newly prepared paracyclophane-containing polymers. For the porphyrin series, a comparison of fully conjugated oligomers exhibiting the general structure (trans-bis(para-ethynyl(zinc(porphyrin)))bis(phosphine)platinum(II))(n) (i.e., the C(6) H(4) group is absent from the main chain) will be made. This contribution also includes a description of the properties of the mononuclear chromophore itself, properties that define those of the polymers. Potential applications with regard to electronic and optical devices will be highlighted. These soluble and stable materials feature both the processing advantages of polymers and the functionality provided by the presence of metal centers. These multifunctional organometallic polyyne polymers exhibit convenient structural variability as well as optical and electronic properties, which renders them important for use in different research domains as chemical sensors and sensor protectors, as converters for light/electricity signals, and as patternable precursors to magnetic metal alloy nanoparticles.

Dual-emissive photoluminescent Langmuir-Blodgett films of decatungstoeuropate and an amphiphilic iridium complex

Langmuir monolayers and Langmuir-Blodgett (LB) films of the decatungstoeuropate [Eu(W(5)O(18))(2)](9-) (EuW(10)) and the amphiphilic Ir complex 1 have been successfully fabricated by using the adsorption properties of the EuW(10) polyanion dissolved in the aqueous subphase onto a positively charged 1 monolayer at the air-water interface. The compression isotherms and Brewster angle microscopy (BAM) of monolayers of 1 on pure water (1 monolayer) and on a subphase containing 10(-6) M EuW(10) and 10(-3) M NaCl (1/EuW(10) monolayer) have been studied. Infrared and UV-vis spectroscopy of the transferred LB films indicate that EuW(10) and 1 molecules are incorporated within these LB films. X-ray reflectivity (SXR) and atomic force microscopy (AFM) experiments indicate that LB films of 1 present a heterogeneous morphology while 1/EuW(10) films show a flatter and more homogeneous surface as well as a layered structure with a periodicity of 4.1 nm. Mixed monolayers of 1 and DODA (dimethyldioctadecylammonium bromide) have been prepared with EuW(10) polyanions in the subphase to control the concentration of 1 and EuW(10) polyanions within the LB films. AFM and SXR experiments with the transferred LB films show that the dilution of 1 with DODA improves the layered structure. The luminescence of 1 is partially quenched by EuW(10) in the 1/EuW(10) LB films, while emission from EuW(10) is not detected. On the other hand, emission from both entities is preserved in the LB films prepared from mixed DODA/1 monolayers, in which the red and yellow emissions arise independently from EuW(10) and 1, respectively. The different DODA:1 ratios lead to changes in the emission color. Therefore, they constitute a promising color-tunable luminescent material.

Organometallic Gold(I) Acetylide/Polyoxometalate Hybrid Langmuir-Blodgett Films: Preparation, Characterization, and Photoelectric Properties

A new series of organometallic/inorganic hybrid Langmuir-Blodgett (LB) films containing an organometallic gold(i) aryleneethynylene metal complex (OMA) as the π-conjugated organometallic molecule and a polyoxometalate (POM, POM = H3BW12O40, H6As2W18O62, or H6P2Mo18O62) of the Keggin and Dawson structure as the inorganic composite, were prepared and characterized by π–A isotherms, UV-vis absorption spectra, photoluminescence spectra, atomic force microscopy imaging, scanning tunnelling microscopy, and surface photovoltage spectroscopy. Our experimental results indicate that stable, well defined and well organized Langmuir and LB films are formed in pure water and polyoxometalate subphases. There is a quenching effect in the luminescence of the gold(i) complex when it is made into the LB films. The OMA/POM hybrid LB films display strong photovoltage effect in the UV-vis region. The photovoltage response of OMA/H6As2W18O62 can be as high as 3338 μV. OMA/POM monolayer films show good electrical conductivity, and the tunnelling current for a OMA/H3BW12O40 monolayer film amounts to 50 to approximately –100 nA when the voltage is set at ±9 V.

Preparation and characterization of Langmuir-Blodgett films of wheel-shaped Cu-20 tungstophosphate and DODA by two different strategies

A novel surfactant-encapsulated organic-inorganic hybrid compound (DODA)(24)Li[Cu(20)Cl(OH)(24)(P(8)W(48)O(184))] x 18 H(2)O (DODA-Cu20) has been prepared from the wheel-shaped tungstophosphate salt K(12)Li(13)[Cu(20)Cl(OH)(24)(H(2)O)(12)(P(8)W(48)O(184))] x 22 H(2)O (Cu20) and dimethyldioctadecylammonium bromide (DODA), and it has been characterized by elemental analysis (EA), thermogravimetric analysis (TGA), (1)H NMR, Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) measurements. Monolayer and multilayer films of DODA-Cu20 were fabricated on different substrates by the Langmuir-Blodgett (LB) technique using H(2)O as the subphase. Another type of organic-inorganic hybrid film, DODA/Cu20, was also deposited on the same substrates as used for the film containing DODA-Cu20 under the same conditions by the LB technique using a Cu20 aqueous solution as the subphase and DODA as the cationic amphiphile for comparison. Both thus-prepared organic-inorganic hybrid films were characterized by UV-vis spectroscopy, XRD, transmission and polarized FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The results indicate that stable monolayers at the air-water interface for DODA-Cu20 and at the air-Cu20 solution interface for DODA can be formed and that two LB films containing DODA-Cu20 and DODA/Cu20 constructed by two different methods both exhibit well-ordered lamellar structures. It is proposed that Cu20 exhibits different packing modes in the two LB films depending on the deposition strategy used.