Solid state physicochemical properties and applications of organic and metallo-organic fullerene derivatives

We review the fundamental properties and main applications of organic derivatives and complexes of fullerenes in the solid-state form. We address in particular the structural properties, in terms of crystal structure, polymorphism, orientational transitions and morphology, and the electronic structure and derived properties, such as chemical activity, electrical conduction mechanisms, optical properties, heat conduction and magnetism. The last two sections of the review focus on the solid-state optoelectronic and electrochemical applications of fullerene derivatives, which range from photovoltaic cells to field-effect transistors and photodetectors on one hand, to electron-beam resists, electrolytes and energy storage on the other.Peer ReviewedPreprin

Orientational relaxations in solid (1,1,2,2)tetrachloroethane

We employ dielectricspectroscopy and molecular dynamic simulations to investigate the dipolar dynamics in the orientationally disordered solid phase of (1,1,2,2)tetrachloroethane. Three distinct orientational dynamics are observed as separate dielectric loss features, all characterized by a simply activated temperature dependence. The slower process, associated to a glassytransition at 156 ± 1 K, corresponds to a cooperative motion by which each molecule rotates by 180° around the molecular symmetry axis through an intermediate state in which the symmetry axis is oriented roughly orthogonally to the initial and final states. Of the other two dipolar relaxations, the intermediate one is the Johari-Goldstein precursor relaxation of the cooperative dynamics, while the fastest process corresponds to an orientational fluctuation of single molecules into a higher-energy orientation. The Kirkwood correlation factor of the cooperative relaxation is of the order of one tenth, indicating that the molecular dipoles maintain on average a strong antiparallel alignment during their collective motion. These findings show that the combination of dielectricspectroscopy and molecular simulations allows studying in great detail the orientational dynamics in molecular solids.Peer ReviewedPostprint (author's final draft

Water-triggered conduction and polarization effects in a hygroscopic fullerene salt

Impedance spectroscopy is employed to probe the frequency-dependent conductivity and dielectric response of the crystalline C60O24Na24 fulleride, both in its pure form obtained by heating to 473 K and in its bulk-hydrate form stable only below 390 K, of chemical formula C60O24Na24 ·16 H2O. A dielectric loss feature is visible in both the pure material and the hydrate, displaying different strength and activated behavior in different temperature ranges.Peer ReviewedPostprint (published version

C60 solvate with (1,1,2)-trichloroethane: dynamic statistical disorder and mixed conformation

We present a full characterization of the orientationally disordered cocrystal of C-60 with (1,1,2)-triChloroethane (C2H3Cl3), by means of X-ray diffraction, Raman spectroscopy, and broadband dielectric spectroscopy. Our results include the determination of molecular con formations, lattice structure, positional disorder, and, molecular reorientational dynamics down to the microsecond time scale. We find that, while in the disordered solid phase of pure C2H3Cl3 the molecules exist only in the gauche conformation, both gauche and transoid conformers are present in the solvate, where they occupy the largest interstitial cavities between the fullerene species. The two C2H3Cl3 conformers exhibit separate, independent relaxations, exhibiting simply activated behavior in the measured temperature range. The relaxation, of the transoid conformer, which has twice the dipole moment of the gmiehe isomer, is significantly slower than that of the latter, due to the high polarizability of C-60 resulting in an electrostatic drag against the reorientations of the dipolar C2H3O3 species. The observation of two distinct, simply activated relaxations freezing at distinct temperatures indicates:that they are not truly many-body relaxations, which may be rationalized considering:that the C2H3Cl3 molecules are separated by the relatively bulky C-60 spacers.Peer ReviewedPostprint (published version

New Porous Heterostructures Based on Organo-Modified Graphene Oxide for CO(2)Capture

In this work, we report on a facile and rapid synthetic procedure to create highly porous heterostructures with tailored properties through the silylation of organically modified graphene oxide. Three silica precursors with various structural characteristics (comprising alkyl or phenyl groups) were employed to create high-yield silica networks as pillars between the organo-modified graphene oxide layers. The removal of organic molecules through the thermal decomposition generates porous heterostructures with very high surface areas (>= 500 m(2)/g), which are very attractive for potential use in diverse applications such as catalysis, adsorption and as fillers in polymer nanocomposites. The final hybrid products were characterized by X-ray diffraction, Fourier transform infrared and X-ray photoelectron spectroscopies, thermogravimetric analysis, scanning electron microscopy and porosity measurements. As proof of principle, the porous heterostructure with the maximum surface area was chosen for investigating its CO(2)adsorption properties

A facile approach to hydrophilic oxidized fullerenes and their derivatives as cytotoxic agents and supports for nanobiocatalytic systems

A facile, environment-friendly, versatile and reproducible approach to the successful oxidation of fullerenes (oxC60) and the formation of highly hydrophilic fullerene derivatives is introduced. This synthesis relies on the widely known Staudenmaier’s method for the oxidation of graphite, to produce both epoxy and hydroxy groups on the surface of fullerenes (C60) and thereby improve the solubility of the fullerene in polar solvents (e.g. water). The presence of epoxy groups allows for further functionalization via nucleophilic substitution reactions to generate new fullerene derivatives, which can potentially lead to a wealth of applications in the areas of medicine, biology, and composite materials. In order to justify the potential of oxidized C60 derivatives for bio-applications, we investigated their cytotoxicity in vitro as well as their utilization as support in biocatalysis applications, taking the immobilization of laccase for the decolorization of synthetic industrial dyes as a trial case.Peer ReviewedPostprint (published version

Guest-molecule dynamics and conductivity effects in carbon-based molecular solids

Disordered systems are abundant in everyday life and so their study is of importance from a scientific and a technological point of view. The most common non-crystalline solid phases are structural glasses (e.g. window glass), in which both translational and orientational degrees of freedom are disordered. While at low temperature (in the glass state) the disorder is static, at higher temperature a viscous state is reached, where the disorder is dynamic (as in a liquid). Other systems exist, namely molecular solids, which display different types of disorder (either static or dynamic depending on temperature) due to the larger variety of microscopic degrees of freedom compared to atomic solids(ch. 1). For instance, molecular solids display phases in which the molecules' average centers of mass occupy lattice positions while their orientations are disordered (orientationally disordered phases). Such phases are usually formed by small molecules or molecules with a globular shape like the carbon-only fullerene molecule (C60). Molecular solids display low electrical conductivities due to localization of valence electrons on single molecules, so that electron hopping is the main charge transport mechanism. The type of disorder, and whether it is static or dynamic, are both factors that have an important impact on the conductivity. This thesis is an experimental study of the dynamic disorder and conduction properties of molecular solids, focusing in particular on hydrated molecular materials and on fullerene systems. The experimental technique of choice, which allows studying simultaneously molecular dynamics and electrical conductivity, is broadband dielectric spectroscopy (ch. 2 and 3). Studying water inside organic systems is of great importance in several contexts, ranging from the study of food texture and the stability of biotechnology products and pharmaceuticals to the investigation of macromolecular function in biochemical systems for which hydration water plays a preeminent role. Fullerene solids are relatively simple systems to study the impact of water and in general of heterogeneous species inside an organic matrix. Hydrophilic or hygroscopic fullerene derivatives can be obtained by functionalization with oxygen or hydroxyl groups, as in the case of the fullerenol molecule (ch. 5). We show in this thesis that water molecules not only display interesting orientational dynamics, but they also contribute to the enhancement of the conductivity due to proton hopping through surface hydration layers. These phenomena are not specific to functionalized fullerenes (ch. 5) but also to other organic materials, as we show for the case of an organic dye of the rhodamine family (ch. 4). As for the dynamics of the fullerene molecules themselves, it is well known that the solid phase of pure C60 exhibits order-disorder orientational transition. We show that a derivative of C60 functionalized with oxygen-containing groups also displays several orientational transitions,reminescent of that of solid C60 (ch. 6). Finally, we analyze the structural and dynamic orientational disorder in a co-crystal of C60 with a small ethane derivative (C60:(1,1,2)-trichloroethane (ch. 7). We are able to observe two distinct orientational dynamics of the ethane molecules. To the best of our knowledge, ours is the first-ever report of the relaxation dynamics of guest molecules intercalated inside C60. Considering the very broad variety of (partially) disordered structures that can be obtained in binary systems containing fullerene molecules, these solids may represent model systems to investigate the impact of disorder and of the interaction geometry on the molecular dynamics of heterogeneous systems. The results of this thesis represent a first step in the direction of extending the current experimental knowledge of disordered solid phases to more complex systems of relevance in organic organic chemistry and biology, or with possible commercial applications.Los sistemas desordenados son muy comunes en nuestra vida cotidiana y su estudio tiene por tanto un impacto importante. Las fases sólidas más comunes son los vidrios estructurales (e.g. los vidrios típicos) en los que tanto los grados de libertad de orientación como de translación están desordenados. A bajas temperaturas (estado vítreo) el desorden es estático, mientras que a temperaturas más altas se alcanza un estado fluido viscoso, donde el desorden es dinámico (como en un líquido). Existen también otros sistemas sólidos, formados por moléculas, que pueden presentar diferentes tipos de desorden (estático o dinámico) debido a la gran variedad de los grados de libertad moleculares en comparación con los sólidos formados exclusivamente por átomos (ch.1). Así existen sólidos moleculares que presentan fases en los que las moléculas tienen movimientos de reorientación manteniendo invariables sus centros de masa (fases orientacionalmente desordenadas). Estas fases pueden estar formadas por moléculas pequeñas o por moléculas con forma globular, como la molécula de fulereno (C60). La baja conductividad eléctrica de los sólidos moleculares es debida a la localización de los electrones de valencia en cada molécula individual, de modo que el mecanismo principal de transporte de carga es el salto (''hopping'') de los electrones entre las moléculas. El tipo de desorden, y si el desorden es estático o dinámico, son factores que tienen un impacto importante en la conductividad del material. Esta tesis es un estudio experimental del desorden dinámico y de las propiedades de conducción en los sólidos moleculares, y está especialmente dirigida al estudio en materiales moleculares hidratados y en sistemas con fulereno. La técnica de caracterización que permite un estudio de la dinámica molecular y de la conductividad eléctrica de manera simultánea es la espectroscopia dieléctrica (ch. 2 y 3). La tesis presta también una especial atención al estudio de la influencia del agua en sistemas orgánicos moleculares, debido a la importancia en muchas aplicaciones, desde la textura de los alimentos, o la estabilidad de productos biotecnológicos, hasta la investigación de la función macromolecular en sistemas bioquímicos, en los que el agua de hidratación tiene un papel fundamental. Los sólidos de fulereno son sistemas sencillos para estudiar el impacto de especies moleculares heterogéneas en el interior de una matriz orgánica. Tanto los derivados higroscópicos como hidrofóbicos del fulereno se pueden obtener por funcionalización con grupos de oxígeno, como en el caso de la molécula de fullerenol (ch. 5). Esta tesis demuestra que las moléculas de agua tienen una dinámica orientacional muy variada y, además, que su presencia contribuye a la conductividad debido a los saltos de los protones a través de los diferentes niveles de hidratación de la superficie. Estos fenómenos se detectan también en otros materiales orgánicos, como es el caso de un colorante orgánico de la familia de la rodamina (ch. 4). En cuanto a la propia dinámica de las moléculas del fulereno, es conocido que la fase sólida de C60 tiene una transición orientacional orden-desorden. De forma paralela, se demuestra la existencia de transiciones similares en un derivado de C60 (oxC60, ch.5). Por último, se estudia también el desorden orientacional, estructural y dinámico, en un cristal mixto formado por C60 y 1,1,2-tricloroetano (ch.7).). En este sistema se observan dinámicas orientacionales asociadas a las conformaciones moleculares del tricloroetano, representando así un estudio sobre la dinámica de moléculas huéspedes intercaladas estructuralmente en una matriz de C60. Los resultados de esta tesis representan un primer paso para profundizar en el conocimiento de sólidos con fases desordenadas y para el progreso en sistemas más complicados y relevantes en el campo de la química y de la biología orgánica, o con posibles aplicaciones comerciales

Solid state physicochemical properties and applications of organic and metallo-organic fullerene derivatives

We review the fundamental properties and main applications of organic derivatives and complexes of fullerenes in the solid-state form. We address in particular the structural properties, in terms of crystal structure, polymorphism, orientational transitions and morphology, and the electronic structure and derived properties, such as chemical activity, electrical conduction mechanisms, optical properties, heat conduction and magnetism. The last two sections of the review focus on the solid-state optoelectronic and electrochemical applications of fullerene derivatives, which range from photovoltaic cells to field-effect transistors and photodetectors on one hand, to electron-beam resists, electrolytes and energy storage on the other.Peer Reviewe

Protonic surface conductivity and proton space-charge relaxation in hydrated fullerol

The ac dielectric properties of both anhydrous fullerol (C-60(OH)(24)) and hydrated fullerol with 20% water mass content are investigated by means of temperature-dependent dielectric spectroscopy. Anhydrous polycrystalline fullerol exhibits charge transport mediated by hopping of electronic charge carriers. Hydrated fullerol has a dc conductivity higher by more than a factor of 10(3) than that of the anhydrous sample due to water-induced proton transport. Four distinct dielectric relaxation processes are observed in hydrated fullerol, two of which lie in the frequency range of the electrode polarization. The fastest relaxation is only observed below the melting point of pure water and is assigned to the migration of hydrogen-bond defects in the physisorbed H2O layers. The other three processes exhibit nonmonotonous temperature dependence upon dehydration by heating. The fastest of the three is present also in the anhydrous powder, and it is assigned to a space-charge relaxation due to accumulation of electronic charge carriers at samples heterogeneities such as grain boundaries. By studying the temperature dependence of the two slower relaxations across dehydration, we identify them as separate electrode polarization effects due to distinct charge carriers, namely electrons and protons. The electronic electrode polarization is also present in pure fullerol, while the proton space-charge relaxation is only present in the hydrated material. Our findings help elucidate the hitherto puzzling observation of more than one nonmonotonous relaxation process in hydrated and water-containing systems