M.V. Russo

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.

Gold nanoparticles and gold nanoparticle-conjugates for delivery of therapeutic molecules. Progress and challenges

This article reviews the most recent literature data on the applications of gold nanoparticles and their various conjugates which make them suitable structures towards biomedical and clinical purposes, with an emphasis on their use as drug delivery vehicles for selective targeting of cancer cells. With the rapid surge in the development of nanomaterials, new methodologies and treatment strategies have been explored and these topics should be taken into consideration when a current scenario is required in the design of new experimental approaches or in a comprehensive data interpretation. We present here a summary of the main properties of gold nanoparticles and their conjugates and the state-of-the-art of non-conventional treatment in targeted drug delivery based on gold nanoparticles as carriers, with the aim to give the reader an overview of the most significant advances in this field.

Dielectric relaxations of ionic thiol-coated noble metal nanoparticles in aqueous solutions: Electrical characterization of the interface

The radiowave dielectric properties of organothiol monolayer-protected Au and Ag metallic nanoparticles have been investigated in the frequency range of 10 kHz to 2 GHz, where a dielectric relaxation, due to the polarization of the ionic atmosphere at the aqueous interface, occurs. The simultaneous measurement of the particle size, by means of dynamic light scattering technique, and of the particle electrical charge, by means of laser microelectrophoresis technique, allow us to describe the whole dielectric behavior at the light of the standard electrokinetic model for charged colloidal particles. Au and Ag metallic nanoparticles experience a large charge renormalization, in agreement with the counterion condensation effect for charged spherical colloidal particles. The value of the effective valence Z(eff) of each nanoparticle investigated has been evaluated thanks to the dielectric parameters of the observed relaxation process and further confirmed by direct current electrical conductivity measurements. All in all, these results provide support for the characterization of the electrical interfacial properties of metallic nanoparticles by means of dielectric relaxation measurements.

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).

HIGH RESOLUTION NEXAFS SPECTROSCOPY STUDY OF GAS-PHASE PHENYLACETYLENE : EXPERIMENT AND THEORY

Abstract Gas phase near-edge X-ray absorption fine structure spectra of phenylacetylene (PA, C 6 H 5 –CCH) have been recorded at the carbon K-edge. The experimental data have been interpreted with the help of ab initio calculations: both the ionisation potentials for the C1s electrons and the theoretical C K-edge absorption spectra have been calculated for all the six inequivalent carbon atoms of PA. A good agreement is observed between experimental and theoretical data, allowing a detailed attribution of the various features in the measured spectrum.