A. Furlani

Thin films of iodine—polyphenylacetylene as starting materials for humidity sensors

Abstract A humidity sensor has been fabricated by using thin films of iodine-doped polyphenylacetylene. The electrical response of the sensor towards relative humidity variations is fast and reversible during long working periods. The investigated sensor is also sensitive to the vapours of other chemical substances.

Synthesis, characterisation and optical properties of symmetrical and unsymmetrical Pt(II) and Pd(II) bis-acetylides. Crystal structure of trans-[Pt(PPh3)2(CC–C6H5)(CC–C6H4NO2)]

Abstract Symmetric trans-[Pt(PPh3)2(CCR)2] and unsymmetrical trans-[Pt(PPh3)2Cl(CCR)], (R=C6H4–pNO2, C6H4–pOCH3), Pt(II) acetylides were prepared and characterised, as well as unsymmetrical Pt(II) bis-acetylides, trans-[Pt(PPh3)2(CCR)(CCR′)], (R=C6H4–pNO2, R′=C6H5; R=C6H4–pOCH3, R′=C6H5; R=C6H4–pOCH3, R′=C6H4–pNO2; R=C6H4–pNO2, R′=[(η5-C5H4)Fe(η5-C5H5)]). Also symmetric Pd(II) bis-acetylides, trans-[Pd(PPh3)2(CCR)2] (R=C6H4–pNO2, C6H5) were synthesised and characterised by IR, NMR, and UV–vis spectroscopies. The optical properties of the new complexes were compared within a series of known Pt(II) complexes containing different phosphines and cis–trans configuration. The absorption and photoluminescence spectra indicate that the emission is found in the range 355–600 nm, depending on the nature of the acetylide ligand bound to Pt. Measurements of SHG for the unsymmetrical bis-acetylides dispersed in polymethylmethacrylate (PMMA) show that the second-order nonlinear optical (NLO) properties depend on the strength of the donor–acceptor substituent of the acetylide ligand. Third-order NLO properties (in particular the nonlinear absorption coefficient α2) were measured by the Z-scan technique; strong push–push and pull–pull substituents on the Pt(II) symmetric bis-acetylides induce electronic delocalisation and tuning of the NLO properties. The single crystal X-ray structure of trans-[Pt(PPh3)2(CC–C6H5)(CC–C6H4NO2)] shows that the unsymmetrical molecule crystallised in the Pbca centric space groups.

Second-harmonic generation and absorption spectra of platinum organometallic complexes incorporated in PMMA films

Pt-acetylides with different end-side groups have been synthesized and incorporated in poly(methylmethacrylate) (PMMA) films for second-order nonlinear optics through high-temperature corona-poling. By using two complementary optical techniques, i.e. in-situ second-harmonic generation (SHG) and angle-resolved spectroscopy, the order parameter and the molecular hyperpolarizability β of the chromophores have been characterized inside the polymer matrix. The relaxation of orientational after order poling fits a bi-exponential equation in agreement with the Debye model for guest/host systems. A comparison with the azo-dye Disperse Red 1 (DR1) is discussed within the two-level model and the role of the platinum moiety for conjugated molecules.

Study of chemical structure and conjugation length in organometallic Pt(II) oligomers and polymers containing 1,4-diethynylbenzene derivatives as bridging units

Abstract The synthesis of platinum containing organometallic rigid rod oligomers and polymers, of general formula—[PtL 2 (CC p C 6 H 4 (2,5-R) 2 CC)] n , where L=PPh 3 , PBu 3; R=H, OC 4 H 9 or OC 16 H 33 , has been carried out. The multinuclear macromolecules have been prepared by the Stille coupling in the extended one pot version. Oligomers of different chain lengths were obtained and fully characterised by means of spectroscopic techniques. Different organic spacers and precursor metal complexes have been employed in order to study and compare the reaction products. Well-defined oligomers were isolated and X-ray photoelectron spectroscopy technique provided information about the chain length and the nature of the end-groups. Luminescence and absorption studies of the newly synthesised Pt based poly-ynes are also reported. A correlation between the chain length, the nature of ligand phosphines and organic spacers with the optical properties was rationalised. The Pt metal centre played an important role in the conjugation, showing a red shift of absorption maxima upon increasing the number of repeating units. Band gaps of about 2.8–3.0 eV were found, corresponding to blue-light emission with a quantum efficiency up to about 3% for measurements performed in solution.

Highly ethynylated polymers: Synthesis and applications for humidity sensors

Abstract The response of two novel ethynylated polymers, poly[1,4-diethynyl-2,5-bis(butyloxy)benzene] (PEBB) and poly[1,4-diethynyl-2,5-bis(octyloxy)benzene (PEOB) to relative humidity (% RH) and alcohols has been investigated. The polymers have been deposited as thin-film membranes on resistive-type devices. PEBB shows a good sensitivity to RH (%) variations in the full range (0–90%), while PEOB is less affected by moisture. Both polymers give a relevant current intensity variation (5 magnitude orders) when exposed to methanol vapours and no response to alcohols with longer alkylic chain was observed. These results suggest that the selectivity of polyynes to hydroxilated molecules can be modulated by the chemical structure, that is in this case by the length of the alkoxy substituents of the benzene moiety in the polymer chain.

Synthesis of highly ethynylated mono and dinuclear Pt(II) tethers bearing the 4,4′-bis(ethynyl)biphenyl (debp) unit as central core

Abstract Mono and bisubstituted bis(ethynyl)biphenyl Pt(II) complexes, i.e. trans- [(RCC)Pt(PPh 3 ) 2 (CC p- C 6 H 4  p- C 6 H 4 CCH)], R= p- NO 2 C 6 H 4 ( 3b ), (η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 ) ( 3c ), and trans -[(RCC)Pt(PPh 3 ) 2 (CC p- C 6 H 4  p- C 6 H 4 CC)Pt(PPh 3 ) 2 (CCR)], R=C 6 H 5 ( 4a ) , p- NO 2 C 6 H 4 ( 4b ), (η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 ) ( 4c ), have been synthesized by the dehydrohalogenation reaction from the appropriate Pt monochloro acetylides trans -[(RCC)Pt(PPh 3 ) 2 Cl], R=C 6 H 5 ( 1a ), R= p- NO 2 C 6 H 4 ( 1b ), R=(η 5 -C 5 H 4 )Fe(η 5 -C 5 H 5 ) ( 1c ) and HCC p -C 6 H 5  p -C 6 H 5 CCH, (4,4′-bis-ethynylbiphenyl), (DEBP) ( 2 ). In order to make possible a direct evaluation of the role of Pt centers on the properties of these highly ethynylated complexes, the corresponding species without Pt were prepared, i.e. C 6 H 5 CCCCC 6 H 4 C 6 H 4 CCCCC 6 H 5 , (4,4′-(bis-phenylethynyl)-diethynylbiphenyl) ( 7 ), and (η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 )(CCCCC 6 H 4 C 6 H 4 CCCC)(η 5 -C 5 H 4 )Fe(η 5 -C 5 H 5 ), (4,4′-(bis-ferrocenylethynyl)-diethynylbiphenyl) ( 8 ). Preparation of the latter compounds was only achieved by the use of the palladium catalyzed Stille coupling reaction, since the dehydrohalogenation route afforded only homocoupled and polymeric products. The electron-donor or electron-withdrawing ligands coordinated to Pt were chosen for the purpose of tuning the optical properties of the complexes through the different charge distribution along the π-electron conjugation. Characteristic spectroscopic features (UV–vis, FT-IR and NMR) of these complexes are discussed.

Iodine-doped polyphenylacetylene thin film as a humidity sensor

Abstract Thin films of iodine-doped polyphenylacetylene (PPA) have been investigated and used as humidity sensors. Measurements of resistance variations of a PPA/I2 system, induced by relative humidity variations ranging from 10 to 90%, have been performed at constant temperatures (25 and 30 °C). The behaviour of the resistance versus relative humidity is found to be approximately exponential. Our samples show a good reversibility during humidity cycles and a relatively fast response time (a few seconds).

Synthesis of some bis(triphenylphosphine)(ethynylferrocenyl) platinum(II) complexes; molecular structure of [PtH(CC-C5H4FeC5H5)(PPh3)2]

Abstract Substituted acetylidoplatinum(II) complexes trans -[PtX(CC-C 5 H 4 FeC 5 H 5 )(PPh 3 ) 2 ] (X  H, Cl, CCPh or CC-C 5 H 4 FeC 5 H 5 ) have been prepared. Controlled basicity of the reaction solutions yields the different complexes. A single-crystal X-ray diffraction study of trans -[PtH(CC-C 5 H 4 FeC 5 H 5 )(PPh 3 ) 2 ] indicates an alternating alignment of the ethynyl ligands between two centrosymmetric platinum atoms, resulting in the formation of a pseudo- polymeric structure.

Synthesis and characterization of poly(ethynyltrimethylsilane) containing Pd(II) coordination sites

Abstract The polymerization of ethynyltrimethylsilane with {Pd[C  C-Si(CH 3 ) 3 )] 2 (PPh 3 ) 2 } in different complex: monomer ratios has been investigated. Polymers containing Pd(II) have been isolated and characterized by means of X.p.s. and FT i.r. measurements. The insoluble polymers obtained contain Pd sites that are σ-bonded to the π-conjugated growth chain and coordinated to the C  C bonds of adjacent chains in a crosslinked structure. The soluble polymers isolated have a linear structure where Pd(II) coordinates through σ-bonds to the polymeric chains and to OPPh 3 ligands. If NHEt 2 is used as the polymerization solvent, substitution of Si(CH 3 ) 3 by N(C 2 H 5 ) 2 groups occurs, catalysed by the Pd complex. Comparison of the X.p.s. and g.p.c. measurements and elemental analyses give an estimation of the number of monomer repeat units for every Pd atom.

Organometallic polymer membrane for gas detection applied to a surface acoustic wave sensor

Abstract The response of a surface acoustic wave (SAW) device towards relative humidity (RH) variations in the range 0–80% has been investigated. The sensor response is very fast and reproducible. The sensitive membrane is a novel organometallic polymer, poly-(bistributylphosphine)-platinum-diethylnylbiphenyl (Pt-DEBP), which has been synthesized and characterized by means of FTIR and XPS measurements.