Rosaria D'Amato

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.

Synthesis and characterisation of bis(ferrocenylethynyl) complexes of platinum (II) A re-investigation of their electrochemical behaviour

Abstract We describe herein the synthesis and the electrochemical behaviour of a series of bis(ferrocenylethynyl) complexes of platinum(II). In all complexes, the electronic interaction between the redox-active iron cores of the ferrocenyl termini is small, indicating a moderate electronic delocalisation over the bis(cyclopentadienyl-acetylide)Pt chain.

Synthesis and properties of p-nitrophenylacetylene–phenylacetylene copolymers

Copolymers of phenylacetylene (PA) and p-nitrophenylacetylene (pNPA) with various monomers ratios were prepared and characterized. The solubility of copolymers is dependent on the number of PA units in the chain. They show a good degree of stereoregularity and the MWs are in the 103–105 a.m.u. range, depending on the monomers and catalyst molar ratios. The soluble samples exhibit film-forming properties and the film-surface morphology may be varied by using different solvents. The copolymers give good electrical response to relative humidity variations.

Static and dynamic light scattering measurements of polyphenylacetylene (PPA) in different organic solvents (tetrahydrofuran, toluene and chloroform)

Abstract The molecular conformation and the behaviour of stereoregular polyphenylacetylene (PPA), prepared by catalytic polymerization in the presence of a Rh(I) complex and dissolved in three different organic solvents (tetrahydrofuran (THF), toluene and chloroform), have been studied by means of static and dynamic light scattering measurements. The results have been compared with those obtained from UV–VIS measurements carried out on the same systems. A very complex phenomenology appears. In THF, the polymer molecular weight, M w , increases with time, remains approximately constant in toluene and decreases in chloroform. On the contrary, the hydrodynamic radius, R H , maintains constant at a value of about 270 nm in THF, while in toluene and chloroform a steady-state condition is reached after 500–1000 min, with a value of the hydrodynamic radius of the order of 150–200 nm. These results suggest that each solvent produces a different effect on the pristine structure of PPA. THF induces the entanglement of the polymer chain and an apparent higher molecular weight, toluene promotes a structural modification, probably a narrow helicoidal red form and chloroform leads to both isomerization and degradation.

Reactivity of the nitro-group of a π-conjugated polymer upon the interface formation with chromium: a photoelectron spectroscopy investigation

Abstract X-ray photoelectron spectroscopy was used in order to investigate the interface formation between chromium and thin films of a newly synthesised π-conjugated polymer P(PA- p NO 2 PA); the investigated material is a block copolymer consisting of phenylacetylene (PA) and para -nitro phenylacetylene ( p NO 2 PA) units {[–(CHC–R) n –(CHC–R′) m –] N ; RC 6 H 5 , R′C 6 H 4 NO 2 }. Chromium was evaporated stepwise in situ onto the polymer surface and the XPS spectra of the substrate polymer and of the metal overlayer were studied as a function of increasing chromium thickness. In the early stages of the interface formation, chromium was found to interact mainly with the nitrogen atoms of the –NO 2 groups, that are reduced to nitride-like species; the N–O bond is broken, as evidenced by the modifications occurring in the N1s and O1s spectra. The changes in the C1s spectra upon increasing metal deposition suggest the formation of a chromium–arene π-complex at low chromium coverage and of carbide-like species at higher chromium thickness.

Energy Dispersive X-ray Diffraction (Edxd) Investigation Of Amorphous Poly(phenylacetylene) (Ppa)

The application of wide-angle x-ray diffraction in energy-dispersive modality (EDXD) to the investigation of the static structure of amorphous poly(phenylacetylene) (PPA) is discussed. The structural investigation was carried out through the systematic comparison of the measured functions (the reduced interference function and the radial distribution function) and the same functions calculated from three-dimensional theoretical models, suitably optimized. Possible configurations and conformations, coming from the combination of the polymeric repeating units, were analyzed separately. Consistent with the literature, a general agreement for a cis-transoidal head-to-tail configuration was achieved. Possible coexistence of trans-transoidal head-to-head with cis-transoidal head-to-tail configuration is also discussed. Several simple models were investigated to gain information about the chain packing. Moreover, a first quantitative investigation of the dependence of the interference function upon mechanical compression of PPA was performed.