Sandra Belviso

Organometallic red-emitting chromophores: a computational and experimental study on cyclometallated Nile Red complexes of palladium(II) and platinum(II) acetylacetonates and hexafluoroacetylacetonates

A comparative photophysical, electrochemical and computational study of a series of Nile Red cyclopalladated and newly synthesised cycloplatinated complexes is reported. All complexes are luminescent at room temperature and the emission properties are governed by the nature of the cyclometallated dye. However, the presence of platinum(II) as metal centre decreases severely the emission quantum yield, while the electronegativity of the ancillary hexafluoroacetylacetonato ligand enhanced the emission properties of the Nile Red complexes.

Synthesis, Spectroscopy and Electrochemistry of Lanthanide Bis-(ethylsulfanyl)tetraazaporphyrins

Reaction of the oespz2− ligand (oespz = 2,3,7,8,12,13,17,18-octakis (ethylsulfanyl)-5,10,15,20-porphyrazinato) with trivalent lanthanide ions, such as Nd3+, Eu3+, Dy3+, Yb3+ and Lu3+, leads to the direct synthesis of the corresponding sandwich complexes, in the radical, ligand-oxidized green form, whereas the reaction with La3+ affords the sandwich complex in the protonated, blue form. It is found that the ligand-oxidized complexes show rather weak electronic absorptions in the range 850–1150 nm and are, compared to lanthanide diporphyrins and diphthalocyanines, very stable both to oxidation and to reduction.

Liaisons between photoconductivity and molecular frame in organometallic Pd(II) and Pt(II) complexes

The synthesis and a comprehensive experimental study of molecular structure, electrochemical properties, photoconductivity, absorption and emission properties of two homologous series of square planar cyclometallated Pd(II) and Pt(II) complexes are described. In these complexes, a five member (C,N) metallacycle is formed by either azobenzene, 2-phenylpyridine or benzo[h]quinoline, while the ancillary (O,N) ligand required to complete the metal coordination sphere is the Schiff base resulting from the condensation of 4-n-hexylaniline with 2-hydroxy-4-n-hexyloxybenzaldehyde. The study is complemented by Density Functional Theory calculations of molecular structure in the ground state, frontier orbitals distribution and energies. Absorption energies, intensities for the transitions and composition of the excited states are characterized by Time Dependent Density Functional Theory computations. Results show that for these complexes the HOMO is located on the Schiff base and the LUMO on the cyclometalated ligand. As also indicated by spectroscopic and photoconductivity results, the photogeneration of charge carriers might be associated with the spatial separation of HOMO and LUMO, while an additional contribution could derive from a conformational variation in the excited state. The separation of the frontier orbitals on different ligands provides simple synthetic routes towards band-gap tuning and energy matching with other molecular species and electrodes, both important features for several applications of molecular semiconductors. The results of the present investigation suggest that these square planar cyclometalated Pd(II) and Pt(II) complexes actually form a new class of photoconductors.

Synthesis, Spectro-Electrochemical Properties and Photoreaction with O2 of Lutetium Bis-ethyltetraazaporphyrin

The synthesis, spectroscopic and electrochemical properties of the Lu(oepz)2 (oepz ≡ 2,3,7,8,12,13,17,18-octakis(ethyl)-5,10,15,20-porphyrazinato) complex are reported. The complex, as inferred from UV-vis spectra recorded at different concentrations, strongly aggregates in solution, the most likely association mode being dimerization. The complex shows a weak near-IR absorption (λmax = 834 nm) that is considerably blue-shifted compared with the near-IR absorption of bis(π-radical) lutetium analogues. The Lu(oepz)2 neutral species is electrochemically stable between 0.73 and -0.98 V (vs Ag/AgCl), which is the largest range of stability for neutral lutetium di- tetrapyrrole complexes. Lu(oepz)2 shows excellent Type II photodynamic activity, as indicated by the value of the singlet oxygen generation quantum yield φΔ of 0.94 obtained by comparison with meso-tetraphenylporphyrin.

Two-electron reduction of alkyl(sulfanyl)porphyrazines: a route to free-base and peripherally metallated asymmetric porphyrazines

Treatment of octakis(octylthio)porphyrazine (H(2)OOSPz) with cis-bis(benzonitrile)dichloroplatinum(II) in a 1,2,4-trichlorobenzene (TCB)-n-BuOH mixture at 190 degree C affords the asymmetric porphyrazine 2H-heptakis(octylthio)porphyrazine, H(2)HOSPz, in ca. 40% yield. In the key synthetic step the two-electron reduced diprotonated porphyrazine, [H(2)OOPz(4-)(H(+))(2)](hemiporphyrazinogen), forms in nearly quantitative yield. This species undergoes nucleophilic substitution of an octylsulfide group by H(-), affording the asymmetric porphyrazine, this process being favoured by the high-temperature induced charge and structural intramolecular rearrangements. The resulting molecule shows mesomorphic behaviour. Interestingly, in the presence of sodium acetate, or in neat TCB, the asymmetric porphyrazine does not form at all. Under these conditions, a PtCl(2) molecular fragment coordinates both to a porphyrazine aza bridge and to a thioether moiety leading to the formation of the [H(2)OOSPz]PtCl(2) complex. The S,N-coordination of the PtCl(2) unit was proved by (1)H, (195)Pt[(1)H], and (13)C NMR spectroscopy, and supported by DFT (B3LYP) calculations. The complex conjugates high asymmetry with strong solvatochromism and, therefore, it is potentially interesting for nonlinear optics.

Columnar Discotic Mesophases from Novel Non-symmetrically Substituted (Octylsulfanyl) Porphyrazines

Synthesis and mesomorphism of novel non-symmmetric mono β-aryl (octylsulfanyl)porphyrazines and their Ni(II) complexes were reported. A recently disclosed asymmetrization procedure led to mono β-bromo substituted porphyrazines, which provided access to aryl substituted derivatives through Suzuki cross-coupling. UV-Vis spectroscopy showed a bathochromic shift for bromine and aryl substituted nickel complexes. Optical Microscopy and DSC showed that Br derivatives 3a–3b and H-heptakis Ni(II) complex 2b display two columnar mesophases (Colh and Colr) stable even at RT and a wide ΔT (100°C). Introduction of the aryl substituent on the macrocycle caused the appearance of only the Colh mesophase and lower ΔT.

Effect of polyfluorination on self-assembling and electronic properties of thioalkyl-porphyrazines

The novel polyfluorinated thioalkyl-porfirazine 2,3,7,8,12,13,17,18-octakis(1,1,1,2,2,-3,3,4,4-nonafluorohexylthio)-5,10,15,20-21H,23H-porfirazine was synthesized to investigate the fluorine effect on self-aggregation, electrochemical, and spectral properties of this class of tetrapyrrole macrocycles. This compound showed an ordered and quite thermally stable columnar discotic mesophase, never seen in non-fluorinated symmetrically substituted “free-base” thioalkyl-porphyrazines, revealing a significant effect of fluorine on molecular self-assembling properties. An important effect of fluorination was also observed on the spectral and electrochemical properties of the molecule, giving rise to a hypsochromic shift in the 400–700 nm range of UV-vis absorption spectrum and to a marked cathodic shift of the reduction potentials in respect to the non-fluorinated analogs. DFT and TDDFT calculations has been undertaken to elucidate the origin of the observed behavior. Interestingly, HOMO, LUMO, and band-gap values together with its mesomorphic properties make this compound a promising material for organic photovoltaics.

Thioethyl‐Porphyrazine/Nanocarbon Hybrids for Photoinduced Electron Transfer

Università degli Studi della Basilicata, Dipartimento di Scienze, via dell’Ateneo Lucano, 10; 85100 Potenza, Italy LASCAMM, CR-INSTM Unità della Basilicata Istituto Italiano di Tecnologia, Graphene Labs, Via Morego 30; 16163 Genova, Italy Università degli Studi di Genova, Dipartimento di Chimica e Chimica Industriale, Via Dodecaneso 3; 16163 Genova, Italy Università degli Studi di Roma “La Sapienza”, Dipartimento di Chimica e Tecnologie del Farmaco, Piazzale Aldo Moro, 5; 00185 Roma, Italy Istituto Italiano di Tecnologia, Nanochemistry Department, Via Morego 30; 16163 Genova, Italy

An Interplay Between Infrared Multiphoton Dissociation Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry and Density Functional Theory Computations in the Characterization of a Tripodal Quinolin-8-Olate Gd(III) Complex

AbstractA new hexadentate, tripodal 8-hydroxyquinoline based ligand (QH3) and its gadolinium(III) tris-chelated (GdQ) complex with hemicage structure was investigated by using high resolution Fourier-transform ion cyclotron resonance mass spectrometry (FTICRMS). The protonated adduct of the free ligand and its hemicage tripodal Gd(III) complex, [GdQ + H]+, were first observed in experiments of electrospray ionization (ESI) with a linear ion trap (LTQ) mass spectrometer and further investigated by using high resolution FTICRMS. Gas-phase dissociation of the protonated Gd(III) complex, by infrared multiphoton dissociation (IRMPD) FTICR MS, demonstrated a fragmentation pattern with six main product cluster ions labeled as [Fn]+ (n = 1 up to 6). These product ions suggest the elimination of 7-amino-alkyl or 7-alkyl chains of the hemicage moiety. High resolution MS conditions allowed the elucidation of the fragmentation pattern and product ion structures along with the determination, among the isotopic pattern of Gd, of the chemical compositions of closely related species, which differ in terms of hydrogen content. Among the Gd six naturally stable isotopes, 158Gd is the most abundant, and its peak within each cluster was used as a reference for distinguishing each product ions. Computational DFT investigations were applied to give support to some hypothesis of fragmentation pathways, which could not have been easily justified on the basis of the experimental work. Furthermore, computational studies suggested the coordination geometry of the protonated parent complex and the five- and four-coordinated complexes, which derive from its fragmentation. Furthermore, experimental and computational evidences were collected about the octet spin state of the parent compound.

Inducing asymmetry in free-base, MnIII, NiII and CuII (ethylsulfanyl)porphyrazines: synthetic aspects and spectro-electrochemical implications

Treatment of 2,3,7,8,12,13,17,18-octakis(ethylsulfanyl)-5,10,15,20-porphyrazine (H2OESPz) with CrCl2 in a 1,2,4-trichlorobenzene–n-BuOH mixture resulted in one ethylsulfanyl branch at the pyrrolic β positions of the macrocycle being replaced by an hydrogen atom with >40% yield. The structure of the asymmetric pyrrolic subunit and of the nearest pyrrolic subunits have been determined by NMR spectroscopy. The reaction path leading to the asymmetric porphyrazine implies the formation of a two-electron reduced diprotonated porphyrazine, [H2OESPz(−4)(2H+)], that, as a consequence of charge and structural intramolecular rearrangements at high temperature, undergoes nucleophilic substitution of an ethyl sulfide group by H−. UV-Vis and near-IR results suggest that the asymmetric substitution modifies the (sulfanyl)porphyrazine π and nSulfur levels. On the contrary, ESR spectroscopy shows that the electronic properties of the coordinated Cu2+ ion are affected only marginally. The half-waves of the ligand first reductive processes sensibly shift towards cathodic potentials in the asymmetric metal porphyrazines, but not in the asymmetric free-base porphyrazine, probably due to conflicting electronic and structural effects induced by removal of an ethylsulfanyl tail.