Francesca Villafiorita-Monteleone

Perylene diimide derivatives as red and deep red-emitters for fully solution processable OLEDs

We report on the photophysical characterization of two solution-processable red-emissive perylene diimide molecules and on their use in fully solution assembled OLEDs. The two emitters contain sterically hindered aromatic naphthalene or acenaphthene substituents on the perylene core. These fused rings limits the perylene diimide intermolecular π–π interactions in the solid state due to highly sterically hindered effects, while preserving an extended conjugation between the substituents and the perylene core. Indeed, these features generate a broad absorption for both perylene derivatives along with an efficient red and deep red emission in the solid state for the PDIs with naphthalene and acenaphthene, respectively. The performances of both emitters were tested on OLEDs, where the active layer is a film of bulk PDI, fabricated by simple solution processing. The devices with acenaphthene-substituted perylene diimide provide deep red electroluminescence with emission wavelength at 690 nm, CIE coordinates of (x = 0.69, y = 0.29) and show the best efficiency reported so far for OLED based on PDI fluorescent emitters.

Nanocomposite Pattern-Mediated Magnetic Interactions for Localized Deposition of Nanomaterials

We present a method to create, align, and locate magnetic wires throughout and on the surface of patterned polymer matrices, following the magnetophoretic transport and self-assembly of ferromagnetic nanoparticles under a static magnetic field during laser photopolymerization of monomer/nanoparticle casted solutions. The resulting films have the ability to attract and immobilize small quantities of magnetic nanomaterials locally on the ferromagnetic wires, as proved by a detailed topography study. Magnetic studies on the films before and after the spontaneous deposition, demonstrate that the deposited nanomaterials alter significantly the magnetic character of the system, making thus possible their macroscopic identification. This offers the possibility to realize sensing devices based on hybrid materials with magnetic properties.

Optically controlled liquid flow in initially prohibited elastomeric nanocomposite micro-paths

The significant increment of TiO2 surface wettability upon UV irradiation makes it a promising component of materials or systems with tunable surface wetting characteristics. This remarkable property of TiO2 is retained in the nanocomposite materials developed for this work, which consist of the elastomer PDMS enriched with organic-capped nanorods of TiO2. In particular, the nanocomposites demonstrate a surface transition from a hydrophobic state to a hydrophilic one under selective pulsed UV laser irradiation. This wettability change is reversible, with the hydrophobic character of the nanocomposites being fully recovered after a couple of days of samples storage in moderate vacuum. The hydrophobic-to-hydrophilic transition and recovery can be repeated tens of times on the same sample without any apparent fatigue. As verified by XPS and AFM analysis, the wettability enhancement is exclusively attributed to the TiO2 nanorods exposed on the nanocomposite surface. The tuning of the surface wettability properties of the PDMS/TiO2 materials, together with the easy processability of this elastomer, opens the way to the realization of microfluidic devices with controlled liquid flow. We demonstrate the potentiality of such systems by fabricating microfluidic channels with walls of PDMS and PDMS/TiO2 nanorods composite materials. The combination of the used geometry with the hydrophobic character of both the pure and nanocomposite PDMS prohibits the penetration of water in their developed microchannels. After UV irradiation, water penetration is allowed inside the irradiated nanocomposite microfluidic channels, whereas it is still forbidden after the irradiation of the bare PDMS microchannels, revealing the essential role of the TiO2 nanofillers.

Highly emissive supramolecular assemblies based on π-stacked polybenzofulvene hosts and a benzothiadiazole guest

Two new benzofulvene derivatives bearing a fluorene chromophore in different positions of the phenylindene scaffold were synthesized and induced to polymerize spontaneously. The photophysical investigation evidenced the role of the substitution topology of the monomeric units in the optical properties of the corresponding polymers. In particular, the polymer emission efficiency was found to improve both in solution and in the solid state when the fluorene residue enhances monomer conjugation and rigidity. The ability of this newly synthesized class of polymers to self-organize in supramolecular structures is evidenced through a study on blends with a benzothiadiazole based dye at different concentrations. Aggregation quenching processes of the dye are sharply reduced and complete resonant energy transfer from the polymer to the dye is reached even at 1% dye concentration. The peculiar ability of this new class of π-stacked polymers to self-assemble in such a supramolecular organization suggests their use as platforms for the design of more complex nanostructured films with enhanced optical and optoelectronic properties.

Controlled Swapping of Nanocomposite Surface Wettability by Multilayer Photopolymerization

Single-layered photopolymerized nanocomposite films of polystyrene and TiO(2) nanorods change their wetting characteristics from hydrophobic to hydrophilic when deposited on substrates with decreasing hydrophilicity. Interestingly, the addition of a second photopolymerized layer causes a swapping in the wettability, so that the final samples result converted from hydrophobic to hydrophilic or vice versa. The wettability characteristics continue to be swapped as the number of photopolymerized layers increases. In fact, odd-layered samples show the same wetting behavior as single-layered ones, while even-layered samples have the same surface characteristics as double-layered ones. Analytical surface studies demonstrate that all samples, independently of the number of layers, have similar low roughness, and that the wettability swap is due to the different concentration of the nanocomposites constituents on the samples surface. Particularly, the different interactions between the hydrophilic TiO(2) nanorods and the underlying layer lead to different amounts of nanorods exposed on the nanocomposites surface. Moreover, due to the unique property of TiO(2) to reversibly increase its wettability upon UV irradiation and subsequent storage, the wetting characteristics of the multilayered nanocomposites can be tuned in a reversible manner. In this way, a combination of substrate, number of photopolymerized layers, and external UV light stimulus can be used in order to precisely control the surface wettability properties of nanocomposite films, opening the way to a vast number of potential applications in microfluidics, protein assays, and cell growth.

Side chain engineering in π-stacked polybenzofulvene derivatives bearing electron-rich chromophores for OLED applications

In order to obtain new polymeric materials endowed with improved optoelectronic performances, suitable side chain engineering was designed to insert different chromophores showing electron donating ability [i.e. triphenylamine (TPA) and 9-methylcarbazole (MCBZ) residues] in two different key positions (i.e. 6 and 4′) of the 3-phenylindene scaffold of the polybenzofulvene monomeric units. Among the four newly-synthesized polybenzofulvene derivatives, those bearing triphenylamine moieties were found to show higher emissive properties with respect to the corresponding carbazole derivatives. Moreover, the preliminary OLED devices prepared with the triphenylamine-based polymers showed promising features, but the role of the aggregation process in affecting the emission properties of poly-6-TPA-BF3k suggested that extensive device development studies are required in order to maximize polybenzofulvene performances in OLED applications.

Development of Imidazole-Reactive Molecules Leading to a New Aggregation-Induced Emission Fluorophore Based on the Cinnamic Scaffold

In order to obtain new fluorophores potentially useful in imidazole labeling and subsequent conjugation, a small series of Morita–Baylis–Hillman acetates (3a–c) was designed, synthesized, and reacted with imidazole. The optical properties of the corresponding imidazole derivatives 4a–c were analyzed both in solution and in the solid state. Although the solutions display a very weak emission, the powders show a blue emission, particularly enhanced in the case of compound 4c possessing two methoxy groups in the cinnamic scaffold. The photophysical study confirmed the hypothesis that the molecular rigidity of the solid state enhances the emission properties of these compounds by triggering the restriction of intramolecular motions, paving the way for their applications in fluorogenic labeling.

Poly-histidine grafting leading to fishbone-like architectures

A small series of Morita–Baylis–Hillman adduct (MBHA) derivatives was synthesized and made to react with imidazole, N-acetylhistidine, and N-acetylhexahistidine as models of poly-histidine derivatives. Intriguingly, the reaction of MBHA derivatives 1a and b with imidazole in acetonitrile–phosphate buffered saline (PBS) gave the imidazolium salt biadducts 3a and b as the main reaction products. These results were confirmed by experiments performed with N-acetylhistidine and 1b and suggested the possible occurrence of these structures in the products of poly-histidine labeling with MBHA derivatives 1a and b. These compounds were then transformed into the corresponding water-soluble derivatives 1c–e by introducing oligo(ethylene glycol) chains and their reactivity was evaluated in preliminary experiments with imidazole and then with N-acetylhexahistidine in PBS. The structure of polymeric materials Ac-His-6-MBHA-1d and Ac-His-6-MBHA-1e obtained using ten-fold excesses of compounds 1d and e was investigated using mass spectrometry, NMR spectroscopy, and photophysical studies, which suggested the presence of biadduct residues in both polymeric materials. These results provide the basis for the preparation of fishbone-like polymer brushes, the characterization of their properties, and the exploration of their potential applications in different fields of science such as in vivo fluorogenic labeling, fluorescence microscopy, protein PEGylation, up to the production of smart materials and biosensors.