Chemical functionalization and characterization of graphene-based materials.

Graphene-based materials (GBMs), with graphene, their most known member, at the head, constitute a large family of materials which has aroused the interest of scientists working in different research fields such as chemistry, physics, or materials science, to mention a few, arguably as no other material before. In this review, we offer a general overview on the most relevant synthetic approaches for the covalent and non-covalent functionalization and characterization of GBMs. Moreover, some representative examples of the incorporation into GBMs of electroactive units such as porphyrins, phthalocyanines, or ferrocene, among others, affording electron donor-acceptor (D-A) hybrids are presented. For the latter systems, the photophysical characterization of their ground- and excited-state features has also been included, paying particular attention to elucidate the fundamental dynamics of the energy transfer and charge separation processes of these hybrids. For some of the presented architectures, their application in solar energy conversion schemes and energy production has been also discussed.

Electroactive carbon nanoforms: a comparative study via sequential arylation and click chemistry reactions.

The reactivity of several carbon nanoforms (CNFs), single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and graphene, has been investigated through a combination of arylation and click chemistry Cu(I)-mediated azide-alkyne cycloaddition (CuAAC) reactions. The approach is based on the incorporation of electroactive π-extended tetrathiafulvalene (exTTF) units into the triazole linkers to modulate the electronic properties of the obtained conjugates. The introduction of strain, by bending the planar graphene sheet into a 3D carbon framework, is responsible for the singular reactivity observed in carbon nanotubes. The formed nanoconjugates were fully characterized by analytical, spectroscopic, and microscopic techniques (TGA, FTIR, Raman, UV-Vis-NIR, cyclic voltammetry, TEM and XPS). In the case of SWCNT conjugates, where the functionalization degree is higher, a series of steady-state and time resolved spectroscopy experiments revealed a photoinduced electron transfer from the exTTF unit to the electron-accepting SWCNT.

Buckyballs.

Buckyballs represent a new and fascinating molecular allotropic form of carbon that has received a lot of attention by the chemical community during the last two decades. The unabating interest on this singular family of highly strained carbon spheres has allowed the establishing of the fundamental chemical reactivity of these carbon cages and, therefore, a huge variety of fullerene derivatives involving [60] and [70]fullerenes, higher fullerenes, and endohedral fullerenes have been prepared. Much less is known, however, of the chemistry of the uncommon non-IPR fullerenes which currently represent a scientific curiosity and which could pave the way to a range of new fullerenes. In this review on buckyballs we have mainly focused on the most recent and novel covalent chemistry of fullerenes involving metal catalysis and asymmetric synthesis, as well as on some of the most significant advances in supramolecular chemistry, namely H-bonded fullerene assemblies and the search for efficient concave receptors for the convex surface of fullerenes. Furthermore, we have also described the recent advances in the macromolecular chemistry of fullerenes, that is, those polymer molecules endowed with fullerenes which have been classified according to their chemical structures. This review is completed with the study of endohedral fullerenes, a new family of fullerenes in which the carbon cage of the fullerene contains a metal, molecule, or metal complex in the inner cavity. The presence of these species affords new fullerenes with completely different properties and chemical reactivity, thus opening a new avenue in which a more precise control of the photophysical and redox properties of fullerenes is possible. The use of fullerenes for organic electronics, namely in photovoltaic applications and molecular wires, complements the study and highlights the interest in these carbon allotropes for realistic practical applications. We have pointed out the so-called non-IPR fullerenes - those that do not follow the isolated pentagon rule - as the most intriguing class of fullerenes which, up to now, have only shown the tip of the huge iceberg behind the examples reported in the literature. The number of possible non-IPR carbon cages is almost infinite and the near future will show us whether they will become a reality.

Tuning the electronic properties of nonplanar exTTF-based push-pull chromophores by aryl substitution.

A new family of π-extended tetrathiafulvalene (exTTF) donor-acceptor chromophores has been synthesized by [2 + 2] cycloaddition of TCNE with exTTF-substituted alkynes and subsequent cycloreversion. X-ray data and theoretical calculations, performed at the B3LYP/6-31G** level, show that the new chromophores exhibit highly distorted nonplanar molecular structures with largely twisted 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) units. The electronic and optical properties, investigated by UV/vis spectroscopy and electrochemical measurements, are significantly modified when the TCBD acceptor unit is substituted with a donor phenyl group, which increases the twisting of the TCBD units and reduces the conjugation between the two dicyanovinyl subunits. The introduction of phenyl substituents hampers the oxidation and reduction processes and, at the same time, largely increases the optical band gap. An effective electronic communication between the donor and acceptor units, although limited by the distorted molecular geometry, is evidenced both in the ground and in the excited electronic states. The electronic absorption spectra are characterized by low- to medium-intense charge-transfer bands that extend to the near-infrared.

Tetrathiafulvalene-based molecular nanowires.

A new molecular wire suitably functionalized with sulfur atoms at terminal positions and endowed with a central redox active TTF unit has been synthesized and inserted within two atomic-sized Au electrodes; electrical transport measurements have been performed in STM and MCBJ set-ups in a liquid environment and reveal conductance values around 10(-2) G0 for a single molecule.