The relaxation dynamics of water in hygroscopic molecular solids is probed by broadband dielectric spectroscopy in the temperature range from 200 to 450 K. Evidence is found for three types of dynamic processes. The intermediate process is common to all probed materials and is associated with the reorientation of bound water molecules that are attached directly onto organic molecules and counterions. A faster process is observed in rhodamine chloride and fullerol, which is the dynamic signature of water in higher hydration layers, either at grain boundaries (rhodamine) or in interstitial clusters (fullerol). All these processes are observed near room temperature and exhibit nonmonotonic temperature dependence and decreasing spectral strength upon heating. In fullerol a third, ultraslow relaxation is observed at high temperature, which may be due to the reorientation of water–fullerol complexes or to the diffusion of water vapor through intermolecular voids.

Impedance spectroscopy is employed to probe the impact of water on the dc conductivity and ac dielectric response of the polycrystalline C 60 (ONa) 24 fulleride, both in its bulk-hydrate form, stable only below 370 K, and in the pure form, obtained by heating to high temperature. Exposure of the pure material to ambient air results in the condensation of water vapor on the crystallites' surface, which in turn leads to an enhancement of the room-temperature conductivity by four orders of magnitude due to charge transport through the hydration layer. Electrical conduction in the hydrate between 320 and 380 K is dominated by a non-equilibrium contribution associated with the structural water, which leads to a value of the dc conductivity that is higher than that of the pure material by almost two decades at 360 K. Both conductivity enhancements are most likely due to a proton exchange mechanism. All impedance spectra exhibit, in the radiofrequency range, a dielectric loss feature related to the accumulation of free charges at grain boundaries, whose strength is strongly affected by the presence of hydration water.

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 waterinduced 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 H 2 O 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 sample's 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.

We employ dielectric spectroscopy 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 glassy transition at 156±1 K, corresponds to a cooperative motion by which each molecule rotates by 180º 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 dielectric spectroscopy and molecular simulations allows studying in great detail the orientational dynamics in molecular solids. 2 INTRODUCTIONWhile conventional (atomic) solids are made of atomic constituents with only translational degrees of freedom, so that their structure is totally determined by translation symmetry and fundamental excitations are vibrational in character, in molecular solids the constituent molecules possess also orientational (as well as internal) degrees of freedom, which lead to a richer variety of possible solid phases and to the existence of rotational excitations such as librations and orientational relaxations. A molecular solid can display complete translational and rotational order, as in a molecular crystal, or complete rototranslational disorder, as in a molecular glass. In between these two extremes, molecular solids also display phases (known as Orientationally disordered (OD) phases are generally formed by relatively small globular molecules such as derivatives of methane, 1,2,3 neopentane, 4 adamantane 5 or fullerene, 6 or by small linear ones such as ethane derivatives 7,8,9 and dinitriles. 10 OD solids exhibit many of the phenomenological features of glass formers, displaying in particular a cooperative rotational motion, called α relaxation, that undergoes a continuous, dramatic slow-down upon cooling, 11,12 leading in some cases to a glass-like 3 transition associated with rotational freezing. 13,14 Contrary to structural glasses, which do not exhibit any long-range order, OD phases are characterized by a translationally ordered structure and can therefore be more thoroughly characterized with the help of methods that exploit the translational symmetry such as Bragg diffraction, lattice models, or solid-state NMR spectroscopy. Even more importantly, since as mentioned OD phases are generally formed by molecular species with a simple structure ...

A facile, environment-friendly, versatile and reproducible approach to the successful oxidation of fullerenes (oxc 60) 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 (c 60) 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 C 60 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.

We present a full characterization of the orientationally disordered co-crystal of C 60 with (1,1,2)-trichloroethane (C 2 H 3 Cl 3 ) by means of x-ray diffraction, Raman spectroscopy and broadband dielectric spectroscopy. Our results include the determination of molecular conformations, lattice structure, positional disorder, and molecular reorientational dynamics down to the microsecond timescale. We find that, while in the disordered solid phase of pure C 2 H 3 Cl 3 the molecules exist only in the gauche conformation, both gauche and transoid conformers are present in the solvate, * Corresponding author. Tel: +34 934016568. E-mail: roberto.macovez@upc.edu. 2 where they occupy the largest interstitial cavities between the fullerenes species. The two C 2 H 3 Cl 3 conformers exhibit separate, independent relaxations, both characterized by simplyactivated behavior. The relaxation of the transoid conformer, which has twice the dipole moment of the gauche 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 C 2 H 3 Cl 3 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 C 2 H 3 Cl 3 molecules are separated by the relatively bulky C 60 spacers.3

Abstract: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.

Interdigital electrodes fabricated by standard lithography on silicon chips are employed to probe the dipolar molecular dynamics and electric conduction properties of thin rhodamine films grown with two different methods. The conductivity is due to electronic charge carriers, and at around room-temperature, it is higher by 1 order of magnitude in solution-deposited films than in thermally evaporated ones. The organic material exhibits two intrinsic dynamic processes, of which the one at higher temperature is due to the orientational motion of the dipole moment of the rhodamine units, while the one at lower temperature is due to the motion of a local dipole associated with the chlorine counterions and is absent in thermally evaporated films. Our results show that thin-film dielectric spectroscopy is an easily implementable and versatile tool to extract valuable information on thin organic films.