Giovanna De Luca

Scaling the Chirality in Porphyrin J-Nanoaggregates

Chiral porphyrin J-aggregates are confined into microemulsions, achieving a fine control of their size and optical properties. The quality of the circular dichroism signal exhibits a remarkable scaling on the dimension from the nano- up to mesoscopic regime.

Self-organizing functional materials via ionic self assembly: porphyrins H- and J-aggregates on synthetic chrysotile nanotubes.

Positively charged, synthetic chrysotile nanotubes act as inorganic tectons supporting H- and J-type aggregates of anionic porphyrins with markedly different optical properties, making these nanohybrid materials of interest for application in nanotechnology.

Solvent vapour annealing of organic thin films: controlling the self-assembly of functional systems across multiple length scales

Solvent vapour annealing allows macroscopic healing of molecular assemblies at surfaces to form suprastructures featuring a higher degree of order, and significant improvement of the performance of organic electronic devices.

Sitting-Atop Metallo-Porphyrin Complexes: Experimental and Theoretical Investigations on Such Elusive Species

The interaction between the sodium cation and two meso-aryl porphyrins (tetraphenylporphyrin, TPP, and tetra(4-methoxyphenyl)porphyrin, TMPP) leads to the formation of new species that have been identified as Sitting-Atop (SAT) complexes, where the metal ion interacts with the N atoms of the porphyrin core without the concomitant deprotonation of the N-H groups. These species have been attained in low polarity solvent through the interaction of the porphyrin free bases with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB), and investigated in situ through a combination of spectroscopic techniques, such as UV/vis absorption and fluorescence (static and time-resolved), resonance light scattering, FT-IR, and (1)H NMR. All spectroscopic evidence points to the occurrence of a single equilibrium between each parent compound and its SAT complex, ruling out the presence of other metallo-, protonated, or aggregated porphyrins in solution. The 1:1 stoichiometry of the adducts has been determined via continuous variation method (Jobs plot), and an estimate of the corresponding association constants in CH(2)Cl(2) at 298 K have been obtained by UV/vis titration (K(eq) = (9 +/- 4) x 10(5) L mol(-1) and (5 +/- 2) x 10(6) L mol(-1) for TPP and TMPP, respectively). Density-functional theory (DFT) calculations on SAT model complexes, [NaTPP(PF(6))] and [NaTMPP(PF(6))], have provided information on the molecular structure of these elusive species and on the nature and strength of the sodium-porphyrin interaction. It is found that the sodium ion is bound to the four nitrogen atoms of the porphyrin core. The involvement of the pyrrolic N atoms results in a modest but not negligible elongation of the N-H bonds, pyramidalization of the hydrogen atoms, and blue shift of the N-H stretching frequencies. Electronic structure and energy decomposition analysis reveal that covalent interactions, mainly consisting of porphyrin to sodium charge transfer interactions, are an important component of the sodium-porphyrin bond. Time-dependent DFT (TDDFT) calculations of the lowest excited states of the model systems provide an unambiguous interpretation of the absorption and emission properties of the experimentally identified SAT complexes.

Phase separation and affinity between a fluorinated perylene diimide dye and an alkyl-substituted hexa-peri-hexabenzocoronene

Fluorination of alkyl groups is a known strategy for hindering miscibility, thus promoting phase separation, when blends are prepared with a hydrocarbon compound. A new perylene bis(dicarboximide) derivative functionalized with branched N-perfluoroalkyl moieties (BPF-PDI) has been synthesized as electron acceptor to be potentially used in conjunction with the electron donor hexakis(dodecyl)hexabenzocoronene (HBC-C12) in bulk heterojunction solar cells. Aiming at controlling self-assembly between the two components at the supramolecular level, stoichiometric blends in CHCl3 have been prepared either by spin- or drop-casting onto silicon surfaces, and further subjected to solvent vapour annealing (SVA) treatment in a CHCl3-saturated atmosphere. Spectroscopic investigation in solution shows the formation of supramolecular BPF-PDI–HBC-C12 dimers, with an association constant Kass = (2.1 ± 0.3) × 104 M−1, pointing to a strong and unexpected affinity between the two species within the mixture. Characterization through optical and atomic force microscopies of the deposited samples revealed that the self-assembly behaviour of the blends on SiOx is remarkably different from mono-component films, thus confirming the absence of a macroscopic phase-separation between the two components featuring isolated domains of the neat acceptor or donor compound. In addition, X-ray studies provided evidence for the existence of a local-scale phase separation. These findings are of importance for organic photovoltaics, since they offer a new strategy to control the phase separation at different scales in electron acceptor–donor blends.

Optical and sensing features of TPPS4 J-aggregates embedded in Nafion® membranes: influence of casting solvents

The tetraanionic water soluble meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) can be easily embedded into Nafion®, obtaining membranes which exhibit interesting optical properties strongly dependent both on the aggregation extent and on the organic solvent used for the re-cast procedure.

Orthogonal self-assembly and selective solvent vapour annealing: simplified processing of a photovoltaic blend

Selective solvent vapour annealing is used on a photovoltaic blend to enhance the interaction between the electron acceptor and the electron donor, simplifying thin films post-processing for photovoltaic applications. A remarkable improvement in the interfacial charge transfer in the bulk hetero-junction is attained, as measured by Kelvin Probe Force Microscopy.

Surface modification and adhesion improvement of polyester films

Facile surface modification of polyester films was performed via chemical solutions treatment. Surface hydrolysis was carried out by means of sodium hydroxide solutions, leading to the formation of carboxylate groups. Three commercial polyester films of 100 μm in thickness were used in this work: AryLite™, Mylar™, and Teonex™, hydrolysis time being the main modification parameter. FTIR-ATR analysis, topography and contact angle (CA) measurements, surface free energy (SFE) and T-Peel adhesion tests were carried out to characterize the modified films. A quantitative estimate of the carboxylates surface coverage as a function of treatment time was obtained through a supramolecular approach, i.e. the ionic self-assembly of a tetracationic porphyrin chromophore onto the film surface. The surface free energy and critical surface tension of the hydrolyzed polyesters was evaluated by means of Zisman, Saito, Berthelot and Owens-Wendt methods. It was shown that NaOH solution treatment increases roughness, polarity and surface free energy of polymers. As a result, T-Peel strengths for modified Mylar™ and Teonex™ films were respectively 2.2 and 1.8 times higher than that for the unmodified films, whereas AryLite™ adhesion test failed.

Self-Assembled Colloidal Photonic Crystal on the Fiber Optic Tip as a Sensing Probe

This paper presents an effective and efficient method to fabricate novel fiber optic sensing probes. The new, simple, and low cost approach is based on a 3-D photonic crystal dielectric structure directly deposited on the tip of a multimode optical fiber through the self-assembly of colloidal crystals (CCs) via a vertical deposition technique. Here, the CC is made of polystyrene nanospheres with 200 nm diameter, and the optical fiber is a UV–vis fiber with a core diameter of 200 μm. The obtained fiber probes exhibit a resonant peak at 480 nm and an amplitude enhancement of 3.7 with respect to the bare fiber; these results are highly repeatable. A numerical tool based on a finite element method analysis has been developed to study and analyze the 3-D subwavelength structures. Numerical results are in good agreement with the observed experimental spectra. Moreover, refractive index measurements have been carried out, revealing a sensitivity of up to 445 nm/RIU in the 1.33–1.36 values range. The achieved performances, which have been obtained by using very small active areas and an easy and reliable fabrication procedure, demonstrate the future perspectives of these fiber-optic probes for chemical and biological sensing applications.

Aggregates of a cationic porphyrin as supramolecular probes for biopolymers

The copper(II) derivative of the dicationic trans-bis(N-methylpyridinium-4-yl)diphenylporphyrin (t-CuPagg) forms large fractal aggregates in aqueous solution under moderate ionic strength conditions. A kinetic investigation of the aggregation process allows for a choice of experimental conditions to quickly obtain stable assemblies in solution. These positively charged aggregates are able to interact efficiently with negatively charged chiral species, (including bacterial spores) leading to induced circular dichroism signals in the Soret region of the porphyrin, now acting as a sensitive chiroptical probe.