Barbara Panunzi

New NLO active cyclopalladated chromophores in main-chain polymers

Abstract Four new OH-functionalized orthopalladated complexes bearing an electron-donor and an acceptor group in a trans -like arrangement with respect to the metal have been prepared and characterized. The ligands are Schiff bases, bound as C,N- or N,O-chelating moieties. Four new polyesters were obtained by polycondensation from the monomeric complexes and pentyloxyterephthaloyl chloride. Two “model” complexes, each one related to one monomer, were also synthetized, in order to obtain further and more detailed characterization data, and in particular to perform measurements of μβ .

Nonlinear optical properties of some side chain copolymers based on benzoxazole containing chromophores

Acrylate-methylmethacrylate copolymers have been synthesized for nonlinear optical applications. Acrylate monomer units are characterized by the presence in the side chain of phenylbenzoxazole groups containing electron donor-electron acceptor substituents. The phase behavior of all polymers has been investigated by DSC, X-ray diffraction and polarizing microscopy: two of them exhibit liquid crystalline behavior of smectic type. For four polymers, nonlinear optical properties have been examined by second harmonic generation measurements on thin films (∼ 1 μm thickness) electrically poled by corona discharge. Second order susceptibility coefficients d33 and average relaxation times 〈τ〉, relative to the time stability of the chromophore poling, have been measured.

Polymers containing substituted 2-phenyl-benzoxazole side-chain groups: Synthesis and phase behavior

SYNOPSIS The synthesis of substituted 2-phenyl-benzoxazoles has been accomplished by ring closure of Schiff bases. The compounds have been used as precursors of acrylic derivatives displaying LC properties : formula chem. R 1 = NO 2 , CN ; R 2 = -OOC-pC 6 H 4 -O(CH 2 ) 6 OOCCH=CH 2 ; R 1 = - OOC - pC 6 H 4 - O(CH 2 ) 6 OOCCH=CH 2 , -N(CH 3 )(CH 2 ) 6 OOCCH =CH 2 ; R 2 = NO 2 Four comb-like homopolymers have been obtained by radical catalysis from the acrylic monomers. The polymers have been characterized by 1 H-NMR, DSC, x-ray diffraction, viscometry, and polarizing microscopy. Three of the polymers exhibit liquid crystalline properties of smectic type.

Iodohydroxylation of alkenes promoted by molecular and hypervalent(III) iodine

Abstract Several iodohydrins are isolated in good yields starting from the corresponding alkenes and a mixture of molecular iodine and phenyliodine(III)bis(trifluoroacetate) (BTI), in CH 3 CN–H 2 O as solvent, at −15°C. Hypoiodous acid is added to the terminal carbon carbon double bond in a Markovnikov fashion. Moreover, the stereochemical features of the products show the anti -stereospecificity of the addition.

The reactivity of furanoid and pyranoid glycals towards aromatic Grignard reagents and a nickel catalyst

Abstract By reaction with aromatic Grignard reagents in the presence of low valent nickel species at low temperature, the 1,2-unsaturated furanoid glycal ( 1 ) undergoes coupling reaction to produce 2,3-unsaturated products ( 1a,b ) as pure stereoisomers. When these reaction conditions are applied to protected 1,2-unsaturated pyranoid glycals ( 2, 3, 4 ), both cross-coupling and elimination reactions occur to give conjugated diene-alcohol derivatives ( 2a; 3a,b; 4a,b , respectively), in moderate yield.

Coordinatively saturated Pt(II) complexes as potential precursors of organometallic polymers

Abstract The synthesis of stable Pt(II) coordinatively saturated derivatives suitable as precursors of organometallic polymers is described. Compounds of the type [PtX 2 (dmphen)(olefin)] (X = CN, SCN; dmphen = 2,9-Me 2 -1,10-phenanthroline) are obtained by oxidative addition to Pt(0) species. The unprecedent fission of activated carbon-carbon bonds to give 18 e − Pt(II) species is described. The solid state structure of [Pt(SCN) 2 (dmphen)(dimethylmaleate)] has been determined by X-ray crystallography. Vinyl monomers [PtCl(RCHCH 2 )(dmphen)(dimethylmaleate)] (R = CO 2 , CH 2 CO 2 ) have also been obtained.

Organometallic polymers containing coordinatively saturated platinum(II) complexes as pendants

Abstract The synthesis and some properties of soluble organometallic polymers which contain trigonal bipyramidal platinum(II) complexes as pendants are described. An N,N-chelate and an olefin define the equatorial plane of the complex, while two anionic ligands, or one anion and a pyridine nitrogen, occupy the axial positions. Each of the coordination sites was used to anchor the organometallic fragments to the polymeric chain.

Origin and fine tuning of the stability of five-coordinated platinum(II) and palladium(II) species. A quantum-mechanical study

Ab initio computations have been performed to characterize the ground state geometries of a number of platinum and palladium complexes [M(N-N) (C2H4)XY] N-N = bidentate N-donor ligand; X,Y = monodentate ligands) and their stability toward the loss of ethylene. The results have been interpreted by an energy component analysis. The computations point out the respective roles of electron donation from ethylene and of back-donation from the metal in determining the relative stabilities of different five-coordinated complexes with respect to their four-coordinated counterparts. Experimental trends are correctly reproduced and interpreted in terms of these two effects. Modifications induced by the deformation energy connected to the addition of a fifth ligand are probably overestimated by our computational model.

Two orthopalladated chromophores

The title compounds, [5-(dimethylamino)-2-[N-(4-methoxyphenyl)iminomethyl]phenyl][N-(4-methoxyphenyl)-4-nitrosalicylaldiminato]palladium(II), [Pd(C14H11N2O4)(C16H17N2O)], (I), and [4-(diethylamino)-N-(4-methoxyphenyl)salicylaldiminato][2-[N-(4-methoxyphenyl)iminomethyl]-5-nitrophenyl]palladium(II) dichloromethane hemisolvate, [Pd(C14H11N2O3)(C18H21N2O2)]*0.5CH2Cl2, (II), both contain push-pull chromophores coordinated to Pd in a square-planar arrangement. In both compounds, the five-membered orthopalladated ring is essentially planar, while the coordinated six-membered ring is not. Deviations from a coplanar arrangement of the phenylene rings of the coordinated Schiff bases are observed in both (I) and (II) as a result of intramolecular steric interactions.

A real-time tripodal colorimetric/fluorescence sensor for multiple target metal ions

Abstract In this work we report on the synthesis of a pyridyl/phenolic/benzothiazole functionalized colorimetric receptor (BPAP) that can selectively recognise Fe(III) and Fe(II) ions in aqueous medium with visible, naked eye colour changes. Moreover, BPAP behaves as a ‘turn-on’ fluorescent chemosensor, showing an excellent sensitivity towards Zn2+ and Cd2+ cations in water by exhibiting fluorometric change. BPAP exhibited a visible detection limit of 5.5 μM and 2.5 μM for Fe3+ and Fe2+, respectively, and a fluorometric selectivity towards Zn2+ and Cd2+ ions with lower detection limits of 205 nM and 642 nM. To understand the mode of binding to the sensor, both the nude sensor and the Zn-complex were isolated and characterized by X-ray crystallography. In Zn-BPAP, the ligand acts as neutral tridentate through Npyridine, Namine and Namide donor atoms. The N atom of benzothiazole group and the OH group of the phenole unit are not coordinated. Computational DFT study was performed on the free ligand BPAP and complex with Zn2+ to investigate the interaction site, to calculate the energies of the frontier molecular orbitals and to corroborate some of the experimental results.