Giacomo Bergamini

Photoinduced reversible switching of porosity in molecular crystals based on star-shaped azobenzene tetramers

The development of solid materials that can be reversibly interconverted by light between forms with different physico-chemical properties is of great interest for separation, catalysis, optoelectronics, holography, mechanical actuation and solar energy conversion. Here, we describe a series of shape-persistent azobenzene tetramers that form porous molecular crystals in their E-configuration, the porosity of which can be tuned by changing the peripheral substituents on the molecule. Efficient E→Z photoisomerization of the azobenzene units takes place in the solid state and converts the crystals into a non-porous amorphous melt phase. Crystallinity and porosity are restored upon Z→E isomerization promoted by visible light irradiation or heating. We demonstrate that the photoisomerization enables reversible on/off switching of optical properties such as birefringence as well as the capture of CO2 from the gas phase. The linear design, structural versatility and synthetic accessibility make this new family of materials potentially interesting for technological applications.

Photoactive Dendrimer for Water Photoreduction: A Scaffold to Combine Sensitizers and Catalysts

We report on the synthesis and characterization of platinum nanoparticles (PtNps) inside the cavities of a PAMAM dendrimer decorated with [Ru(bpy)3](2+) units at the periphery. The phosphorescent ruthenium complexes are used as signaling units of the Pt(2+) complexation in the dendritic architecture and as photosensitizer units in the photocatalytic production of H2 from water. This is the first example of water photoreduction in which the catalyst and the sensitizer are anchored on a dendritic molecular scaffold. This study provides a new outlook in the design of new supramolecular systems and materials for developing artificial photosynthesis.

Bispidines for Dual Imaging

The efficient transformation of the hexadentate bispidinol 1 into carbamate derivatives yields functional bispidines enabling convenient functionalization for targeted imaging. The BODIPY-substituted bispidine 3 combines a coordination site for metal ions, such as radioactive (64) Cu(II) , with a fluorescent unit. Product 3 was thoroughly characterized by standard analytical methods, single crystal X-ray diffraction, radiolabeling, and photophysical analysis. The luminescence of ligand 3 was found to be strongly dependent on metal ion coordination: Cu(II) quenches the BODIPY fluorescence, whereas Ni(II) and Zn(II) ions do not affect it. It follows that, in imaging applications with the positron emitter (64) Cu(II) , residues of its origin from enriched (64) Ni and the decay products (64) Ni(II) and (64) Zn(II) , efficiently restore the fluorescence of the ligand. This allows for monitoring of the emitted radiation as well as the fluorescence signal. The stability of the (64) Cu(II) uf8ff3 complex is investigated by transmetalation experiments with Zn(II) and Ni(II) , using fluorescence and radioactivity detection, and the results confirm the high stability of (64) Cu(II) uf8ff3. In addition, metal complexes of ligand 3 with the lanthanide ions Tb(III) , Eu(III) , and Nd(III) are shown to exhibit emission of the BODIPY ligand and the lanthanide ion, thus enabling dual emission detection.

Luminescent multi-terpyridine ligands: towards 2D polymer formation in solution

The investigated multiterpyridine chromophores form a 2D network upon metal ion complexation that causes profound changes to their photophysical properties; the experimental results are complemented by modeling of the electronic properties of isolated monomers as well as the structure of the polymeric network.

A tailored RAFT copolymer for the dispersion of single walled carbon nanotubes in aqueous media

The Reversible Addition-Fragmentation chain-Transfer (RAFT) synthesis of poly(glycidyl methacrylate) (PGMA) copolymers followed by the post-polymerisation treatment with morpholine allows the rational design of amphiphilic block copolymers that are capable of efficiently dispersing single walled carbon nanotubes (SWCNTs) in aqueous media, as shown by comparative photophysical characterisation and AFM analysis.

Uniform Functionalization of High-Quality Graphene with Platinum Nanoparticles for Electrocatalytic Water Reduction.

Graphene–metal composites have potential as novel catalysts due to their unique electrical properties. Here, we report the synthesis of a composite material comprised of monodispersed platinum nanoparticles on high-quality graphene obtained by using two different exfoliation techniques. The material, prepared via an easy, low-cost and reproducible procedure, was evaluated as an electrocatalyst for the hydrogen evolution reaction. The turnover frequency at zero overpotential (TOF0 in 0.1u2009m phosphate buffer, pHu20056.8) was determined to be approximately 4600u2005h−1. This remarkably high value is likely due to the optimal dispersion of the platinum nanoparticles on the graphene substrate, which enables the material to be loaded with only very small amounts of the noble metal (i.e., Pt) despite the very highly active surface. This study provides a new outlook on the design of novel materials for the development of robust and scalable water-splitting devices.

A Highly Luminescent Tetramer from a Weakly Emitting Monomer: Acid- and Redox-Controlled Multiple Complexation by Cucurbit[7]uril

The tetrahedral, shape-persistent molecule 1(4+), containing four pyridylpyridinium units connected through a central carbon atom, exhibits unexpected photophysical properties including a substantially redshifted absorption (2350u2005cm(-1)) and a very strong fluorescence (Φem = 40u2009%), compared with the monomer 2(+) (Φem = 0.4u2009%). Density functional theory calculations on the structure and spectroscopic properties of 1(4+) and 2(+) show that exciton interactions, homoconjugation, and orbital nature account for the observed differences in their photophysical properties. The protonated tetramer binds four cucurbit[7]uril molecules and the host/guest interactions can be controlled by chemical (acid/base) as well as redox stimuli.

Blue and highly emitting [Ir(IV)] complexes by an efficient photoreaction of yellow luminescent [Ir(III)] complexes

A family of cyclometalated [Ir(III)] complexes containing two F2ppy ligands and a bis-oxazoline (box) ancillary ligand, either chiral (1) or achiral (2) has been synthesized. They exhibit photophysical and electrochemical properties quite similar to the isoelectronic and well known [Ir(F2ppy)2(acac)] complex. However, an unprecedented photoreactivity has been observed. Upon UV irradiation of air-equilibrated solutions of both complexes, stable photoproducts containing an [Ir(IV)] metal center are obtained. The photoproducts exhibit highly efficient blue luminescence with good OLED performances. The same [Ir(IV)] complexes are obtained also by electrochemical oxidation.