Pierluigi Quagliotto

Enhancing the efficiency of a dye sensitized solar cell due to the energy transfer between CdSe quantum dots and a designed squaraine dye

The power conversion efficiency of a dye-sensitized solar cell with tailored squaraine dye enhanced by 47%, due to Forster resonance energy transfer from CdSe quantum dots to the squaraine dye. The incident photons to collection efficiency of electrons indicate panchromatic response from the visible to the near-infrared spectrum.

Reactivity and effects of cyclodextrins in textile dyeing

Abstract Four- to 10-fold improvement of colour uniformity and minor changes of colour yield have been found upon dyeing Nylon 66 and microfiber Nylon 6 fabrics in the presence of cyclodextrin compared to dyeing without it. 1 H NMR data supported the role of cyclodextrin as dye complexing agent. Product quality, however, was also dependent on fabric nature, since for conventional Nylon 6, color uniformity was not improved by the presence of cyclodextrin systems.

Synthesis and properties of cationic surfactants with tuned hydrophylicity

A series of pyridinium-based cationic surfactants has been synthesised and their amphiphilic properties have been studied by conductivity and surface tension measurements. The modification of the substitution pattern on the pyridinium ring by hydrophobic moieties (methyl vs. hydrogen and presence or not of condensed benzene ring) gave the opportunity to investigate structure-activity relationships. Characterization by conductivity and surface tension measurements shed light on the behaviour at the air/water interface and in the micellar environment. In particular, the tendency to form ion pairs at very low concentration was evidenced for all the surfactants substituted on the ring, but not for the simple pyridinium ones. The formation of ion pairs affects both the conductivity and the surface tension plots, showing that a series of steps is involved during the adsorption to the air/water surface. An attempt was made to qualify the single steps in the adsorption at the surface layer. Those steps were attributed to different chemical species (free surfactant ions or ion pairs) and to different arrangements of the surfactant. This work also represents a contribution of investigation at very low surfactant concentrations and high surface tension values.

Microwave-Assisted Synthesis of Near-Infrared Fluorescent Indole-Based Squaraines

A microwave-assisted method for the preparation of a wide color range of 2,3,3-trimethylindolenine-based squaraines and their intermediates is described. This practical approach allows the rapid preparation of both symmetrical and nonsymmetrical squaraine dyes, reducing reaction time from days to minutes with more than 2-fold improvement in product yields when compared to conventional methods.

Effects of additives on the dyeing of nylon-6 with dyes containing hydrophobic and hydrophilic moieties

Abstract A series of azo disperse dyes with variable hydrophobic chain length and hydrophilic (hydroxy or glucosyl group) head were synthesised. 1 H and 13 C NMR spectra indicated that the glucosyl moiety was linked to the azo structure with a β anomeric bond. The dyeing properties on polyamide fibres were assessed with dyeing isotherms and Linitest experiments. The positive effects of additives, as ternary systems (SDS, Brij 35 and octanol) or cyclodextrins, on the dyeing uniformity were shown by tristimulus colorimetry.

Thermodynamic properties of aqueous micellar solutions of N-(1H,1H,2H,2H perfluorooctyl)pyridinium chloride and N-(1H,1H,2H,2H perfluorodecyl)pyridinium chloride

Abstract The thermodynamic properties of aqueous solutions of the cationic surfactants N-(1H,1H,2H,2H perfluorooctyl) pyridinium chloride (OctylPFPC) and N-(1H,1H,2H,2H perfluorodecyl) pyridinium chlorides (DecylPFPC), recently synthesized by us, are reported here for the first time and compared with those of the corresponding N-alkylpyridinium and N-alkylnicotinamide halides. Enthalpies of dilution, densities and osmotic coefficients have been measured as a function of concentration. The results have been expressed in terms of partial molar quantities. Micellization parameters have been obtained by using the pseudophase transition approach. The differences in thermodynamic parameters of micellization between fluorinated surfactants and their protiated counterparts confirm the more pronounced hydrophobic character of the perfluoroalkane moiety, due to the positive free energy of transferring the CF2 group from the singly dispersed to the micellar state, which is higher than that of the CH2 group. The results reported here lead to the following suggestions: (i) the additivity rule can be applied also to a homologous series of partially fluorinated cationic surfactants; (ii) the factor 1.5 between CH2 and CF2 groups obtained from the micellization free energy cannot be transferred to other thermodynamic properties and, in particular, the micellization process is determined by a different balance between entropic and enthalpic factors; (iii) a simple scale factor, taking into account the different steric hindrances of fluorine and hydrogen atoms, is not enough to explain all the thermodynamic properties of cationic fluorinated surfactant solutions.

Disperse and cationic azo dyes from heterocyclic intermediates

Abstract A series of aminophenyl-X-azolopyridines were diazotized and coupled to N,N-diethylaniline. The resulting disperse dyes showed a great versatility towards different fibres such as polyamide polyester and cellulose acetate. The disperse dyes were transformed into cationic dyes by reaction with methyl iodide. The quaternized dyes dyed polyacrylonitrile fibres with excellent uniformity without using a retarding agent. Physical and spectroscopic parameters fastness on dyed fabrics and colour data were correlated with the structure of the dyes. Two-dimensional proton-NMR NOESY experiments were useful for the assessment of particular structures.

Thermodynamics and biological properties of the aqueous solutions of new glucocationic surfactants.

Thermodynamic properties of aqueous solutions of newly synthesized compounds, namely, N-[2-(beta-D-glucopyranosyl)ethyl]-N,N-dimethyl-N-alkylammonium bromides with hydrophobic tails of 12 (C12DGCB) and 16 (C16DGCB) carbon atoms, determined as a function of concentration by means of direct methods, are reported here. Dilution enthalpies, densities, and sound velocities were measured at 298 K, allowing for the determination of apparent and partial molar enthalpies, volumes, and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudophase-transition approach. From a comparison with the corresponding acetylated compounds N-[2-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)ethyl]-N,N-dimethyl-N-dodecylammonium bromide (C12AGCB) and N-[2-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyanosyl)ethyl]-N,N-dimethyl-N-hexadecylammonium bromide (C16AGCB), the role played in the micellization process by the acetylated glycosyl moiety was inferred: it enhances the hydrophobic character of the molecule and lowers the change in enthalpy of micelle formation by about 1.5 kJ mol(-1). By comparing the volume of C12DGCB with those of DEDAB and DTAB, the volumes taken up by the (beta- d-glucopyranosyl)ethyl and beta- d-glucopyranosyl groups were found to be 133 and 99 cm3 mol(-1), respectively. Regarding the interaction with DPPC membranes, it seems that the sugar moiety of the hexadecyl deacetylated compound gives rise to hydrogen bonds with the oxygen atoms of the lipid phosphates, shifting the phase transition of DPPC from a bilayer gel to a bilayer liquid crystal to lower temperatures. C16AGCB induces significantly greater changes than C16DGCB in the structure of liposomes, suggesting the formation of domains. The interaction is strongly enhanced by the presence of water. Neither compound interacts strongly with DNA or compacts it, as shown by EMSA assays and AFM images. Only C16AGCB is able to deliver little DNA inside cells when coformulated with DOPE, as shown by the transient transfection assay. This might be related to the ability of C16AGCB to form surfactant-rich domains in the lipid structure.

Kinetic evidence for the solubilization of pyridine-2-azo-p-dimethylaniline in alkanediyl-α,ω-bis(dimethylcetylammonium nitrate) surfactants. Role of the spacer chain length

The incorporation of the bidentate ligand pyridine-2-azo-p-dimethylaniline (PADA) into micellar aggregates of the dimeric cationic surfactants propanediyl-, hexanediyl- and dodecanediyl-α,ω-bis(dimethylcetylammonium nitrate) (16-3-16,2NO3−, 16-6-16,2NO3− and 16-12-16,2NO3−, respectively) has been studied at 25°C by examining the kinetics of the complexation reaction of the Ni(II) ion with this ligand. For comparison, cetyltrimethylammonium nitrate (CTAN), which can be considered as the “monomeric” surfactant of 16-3-16,2NO3−, has also been used. The kinetic data have shown that, for 16-3-16,2NO3− and CTAN, at a surfactant concentration below the critical micelle concentration (cmc) the rate of the complex formation reaction does not significantly depend on the surfactant concentration, while it slightly decreases in the presence of the other two gemini surfactants. Beyond this critical value, in all cases examined, the rate constant is conspicuously inhibited by the presence of surfactant. The results below the cmc have been explained in the light of conductometric measurements, which have evidenced that both 16-6-16,2NO3− and 16-12-16,2NO3− form premicellar aggregates while 16-3-16,2NO3− and CTAN do not. The kinetic data above the cmc conform to a reaction mechanism that implies partitioning of the ligand only between the aqueous and the micellar pseudo-phases. The quantitative analysis of the kinetic data allows us to estimate the binding of PADA to the cationic micellar aggregates used. Solubilization of PADA in the micelles markedly depends on the nature of the surfactant used and, in particular, decreases on either increasing the spacer chain length or changing the surfactant type, namely conventional or gemini. These trends have been ascribed to the change in the shape of the micellar aggregates and, consequently, the hydrophobic character of the micelles, which can be modulated either by insertion of the spacer in the micellar interior or by using a conventional surfactant. The incremental free energy of transfer of a methylene group in the spacer chain from the aqueous to the micellar pseudo-phase has also been determined. The present data evidence that binding of PADA to micellar aggregates is primarily governed by hydrophobic interactions and the solubilization capability of gemini aggregates is superior to that of conventional micelles.

Terpyridine and Quaterpyridine Complexes as Sensitizers for Photovoltaic Applications

Terpyridine and quaterpyridine-based complexes allow wide light harvesting of the solar spectrum. Terpyridines, with respect to bipyridines, allow for achieving metal-complexes with lower band gaps in the metal-to-ligand transition (MLCT), thus providing a better absorption at lower energy wavelengths resulting in an enhancement of the solar light-harvesting ability. Despite the wider absorption of the first tricarboxylate terpyridyl ligand-based complex, Black Dye (BD), dye-sensitized solar cell (DSC) performances are lower if compared with N719 or other optimized bipyridine-based complexes. To further improve BD performances several modifications have been carried out in recent years affecting each component of the complexes: terpyridines have been replaced by quaterpyridines; other metals were used instead of ruthenium, and thiocyanates have been replaced by different pinchers in order to achieve cyclometalated or heteroleptic complexes. The review provides a summary on design strategies, main synthetic routes, optical and photovoltaic properties of terpyridine and quaterpyridine ligands applied to photovoltaic, and focuses on n-type DSCs.