Francesco Galeotti

Broadband and crack-free antireflection coatings by self-assembled moth eye patterns.

We report broadband and quasi-omnidirectional antireflective (AR) structures inspired to the nipple arrays of moth eyes. These nanocoatings, based on thin elastomeric films, are prepared by simple self-assembly processing of a co-polymer specifically designed to this purpose, and PDMS replica molding. Typically, their surface is covered by a compact distribution of hemispherical nanodomes of about 250 nm in diameter and about 100 nm in height. When these novel nanostructures are applied on a single glass surface, a maximum of 2% transmission enhancement (equivalent to a 50% reduction of the reflected component) towards wavelengths ranging from visible to near IR region is obtained. A considerable AR power is observed also at a wide range of incident angles ranging from normal to 50°. These properties could be attributed to an optimized graded refractive index profile resulting from the randomly distributed and close-packed nanodomes. Moreover, thanks to their elastomeric nature, these crack-free films can be easily applied on glass, as stickers, and periodically replaced, thus offering the possibility of easy dirt removal from an optical device.

Precise surface patterning of silk fibroin films by breath figures

Silk produced by the silkworm Bombyx mori has gained a second youth as a sustainable material for high-technology applications. Here, we report a simple and cost-effective fabrication technique which allows the preparation of free-standing micropatterned pure protein films under ambient processing conditions. In this view, we take advantage of the auto organization of polymers in microporous films - the so-called breath figure formation - to create a specific morphology, which is then transferred to silk. The method includes, after the construction of a microcavity array, two to four soft-lithographic steps, depending on the desired surface patterning. Arrays of concave or convex microlenses, as well as packed micrometric bumps ordered in a hexagonal fashion, are possible obtainable architectures. Despite the straightforwardness of the procedures proposed, our method is able to produce, with high precision, transparent and stable silk fibroin films shaped with an ordered superficial pattern, which are attractive for the development of new biocompatible photonic devices.

Perfluorinated polymer with unexpectedly efficient deep blue electroluminescence for full-colour OLED displays and light therapy applications

The fluorinated phenylene unit is used as a building block for an all-conjugated fluorene-based alternating copolymer (PFO–TFP). The synthesis, carried out by an optimized Suzuki cross-coupling, produces an extremely high purity compound with a series of intriguing properties. Firstly, a blue-shift of the absorption and emission spectra with respect to the parent polymer is achieved. Secondly, the photoluminescence (PL) quantum yields (QYs) of the solution, as high as 68%, are surprisingly retained in the solid-state. Finally, an improved colour stability of the film with respect to unsubstituted polymers, investigated by means of cyclic voltammetry and exposure to ultraviolet radiation, is observed. The PFO–TFP tested as an undoped active layer in a polymer light-emitting diode (PLED) shows a highly desirable pure deep blue 405 nm electroluminescence, CIE = (0.17; 0.06) and a remarkable 5.03% external quantum efficiency, thus fulfilling the requirements for both full-colour displays and biomedical applications. To date, fluorine atom incorporation has been successfully employed in the synthesis of high-performing polymers for organic field-effect transistors and photovoltaics. We give the first unambiguous proof of its efficacy in achieving pure deep blue electroluminescence in a highly efficient and stable PLED, which is competitive with the best reported conjugated oligomer-based devices.

A controlled approach to iron oxide nanoparticles functionalization for magnetic polymer brushes

In this article, we report a detailed study of surface modification of magnetite nanoparticles by means of three different grafting agents, functional for the preparation of magnetic polymer brushes. 3-Aminopropyltriethoxysilane (APTES), 3-chloropropyltriethoxysilane (CPTES), and 2-(4-chlorosulfonylphenyl)ethyltrichlorosilane (CTCS) were chosen as grafting models through which a wide range of polymer brushes can be obtained. By means of accurate thermogravimetric analysis a good control over the amount of immobilized molecules is achieved, and optimal operating conditions for each grafting agent are consequently determined. Graft densities ranging from approximately 4 to 7 molecules per nm(2) are obtained, depending on the conditions used. In addition, the surface-initiated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) carried out with CTCS-coated nanoparticles is presented as an example of polymer brushes, leading to a well-defined and dense polymeric coating of around 0.6 PMMA chains per nm(2).

Nanophase Separation in Polystyrene-Polyfluorene Block Copolymers Thin Films Prepared through the Breath Figure Procedure

The amphiphilic block copolymer formed by a hydrophobic body of polystyrene and a hydrophilic head of poly[9,9-di(2-(2-tetrahydropyranyl-oxy)hexyl)fluorene-alt-9,9-dioctylfluorene] was synthesized, and its solution was used to create thin films with ordered pattern of holes, by means of the breath figure technique. These porous films, after a thermal treatment, were found to show ordered aggregates of the pi-conjugated blocks in the place of the cavities. This is probably due to a preorganization of the two different blocks of the copolymer occurring during the breath figure formation, which is driven by the condensation of water microdroplets on the polymer solution, and to a following phase segregation occurring during the thermal annealing. This approach is a promising tool to be employed for the organization of organic materials at the micro and nanoscale.

The Ferrocenylethynyl Unit: a Stable Hormone Tag

We prepared the organometallic complex 17α-(ferrocenylethynyl)estradiol (=[(3,17β-dihydroxyestra-1,3,5(10)-trien-17α-yl)ethynyl]ferrocene; FcEE; 1) by a novel synthetic method. This metallocene possesses sufficient stability in aqueous media to permit the study of its biological properties. Thus, we were able to show that, despite the addition of a bulky substituent at the 17α position of the steroid, the metallocene is still well- recognized by an antibody specific to estradiol (CR=40%) and by both subtypes (ERα, ERβ) of the estrogen receptor (at 0°, RBA=28 and 37%, resp.). A DCI-MS study of the stability of the carbocation [FcEE−OH]+ showed moderate stabilization of the carbocation, in agreement with the pK value of −0.72 found for the metallocene by means of Denos method. The presence of the ferrocene allows the electrochemical detection of FcEE (1) by HPLC-ED, with a detection limit of ca. 1 nM, suitable for quantitative pharmacological analysis.

High-Efficiency All-Solution-Processed Light-Emitting Diodes Based on Anisotropic Colloidal Heterostructures with Polar Polymer Injecting Layers

Colloidal quantum dots (QDs) are emerging as true candidates for light-emitting diodes with ultrasaturated colors. Here, we combine CdSe/CdS dot-in-rod heterostructures and polar/polyelectrolytic conjugated polymers to demonstrate the first example of fully solution-based quantum dot light-emitting diodes (QD-LEDs) incorporating all-organic injection/transport layers with high brightness, very limited roll-off and external quantum efficiency as high as 6.1%, which is 20 times higher than the record QD-LEDs with all-solution-processed organic interlayers and exceeds by over 200% QD-LEDs embedding vacuum-deposited organic molecules.

Unsoluble ordered polymeric pattern by breath figure approach

Herein, the ability of an alternated polyfluorene copolymer (PFOTHP) bearing tetrahydropyranyl groups on its lateral chains to turn into a solvent resistant material after a thermal treatment is exploited for the fabrication of versatile micropatterned thin films. Nanoporous films are formed by casting PFOTHP from a volatile solvent solution in the presence of humidity. The use of polydimethylsiloxane as a template of the hexagonal pattern enables the retention of structure during the thermal annealing which triggers the formation of unsoluble highly ordered honeycomb structured films. This prevents any restriction in the use of polymeric porous films together with organic solvents. Solutions of a second polymer can be drop on top of these films without modifying their porous surface, so that bicomponent arrays of two different photoluminescent polymers are achievable. The straightforwardness of this approach suggests interesting perspectives in the field of micro and nano-organized materials and offers valuable opportunities of application not only in optoelectronic but also in bioanalysis devices.

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.

CdTe nanocrystal assemblies guided by breath figure templates

We successfully utilized the breath figure (BF) technique to create thin polystyrene films exhibiting, on the surface, holes of a few micrometres of diameter, arranged in hexagonal packed array. Three-dimensional CdTe microporous structures have been obtained by dipping these BF films into an aqueous solution of CdTe nanocrystals, and stabilized by thermal treatment. The resultant hybrid film joins together the morphology feature of polymeric breath figures and the photoluminescence feature of the semiconducting nanoparticles. In addition, micrometric disk-shaped CdTe aggregates have been anchored in hexagonal fashion to a silicon substrate, which has previously been imprinted with a hydrophilic/hydrophobic pattern. These patterned surfaces made of assembled quantum dots are promising tools for a variety of applications including light-emitting devices and hybrid organic/inorganic solar cells.