Embedding Fullerenes in Thin Sol-Gel Films
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MAURIZIO PRATO*, MICHELE MAGGINI,** GIANFRANCO SCORRANO,** GIOVANNA BRUSATIN,*** PLINIO INNOCENZI,*** MASSIMO GUGLIELMI,*** MORENO MENEGHETII,**** RENATO BOZIO**** *Dipartimento di Scienze Farmaceutiche, UniversitA di Trieste, Piazzale Europa 1, 34127 Trieste, Italy "**Centro Meccanismi di Reazioni Organiche del CNR, Dipartimento di Chimica Organica, Via Marzolo 1, 35131 Padova, Italy ***Dipartimento di Ingegneria Meccanica, Settore Materiali, Via Marzolo 9, 35131 Padova, Italy ****Dipartimento di Chimica Fisica, Universitb di Padova, Via Loredan 2, 35131 Padova, Italy
ABSTRACT Fullerene C60 can be considered an interesting molecule for the preparation of new materials with attractive optical properties. In the present work we report the preparation of sol-gel derived, glass-like materials containing C60 and a C60 derivative prepared by 1,3-dipolar cycloadditions of azomethine ylides to C60. The optical characterisation of the films confirms the presence of C60 and its derivative, in the glass matrix.
The properties of buckminsterfullerene (C6 0) [1,2] have attracted much interest, in the last few years, in materials science and technology [3-6]. Among the most notable features of C60 , are its optical properties [7,8], which make this molecule interesting from the point of view of non-linear optical materials [9], as is shown, for example, in optical limiting experiments [ 10]. The most promising materials for optical limiting are in fact those which, owing to excited state absorption, the transmittance decreases with increasing laser fluence [11]. For such applications it would be desirable to include C60 by simple method in thin films with waveguiding properties and good resistance against environmental degradation. These requirements can be satisfied by using composite systems. In this respect, the sol-gel processing is an attractive possibility, mainly due to the relatively low temperatures at which inorganic or hybrid organic-inorganic glasses can be prepared [12]. The homogeneous inclusion of organic molecules in a sol-gel matrix requires the solubility of the compound in a solvent suitable for sol-gel processing. The best thing would be to use a 351 Mat. Res. Soc. Symp. Proc. Vol. 359 01995 Materials Research Society
single common solvent for the three main species, i.e. alkoxide, water and the organic compound, but it is also possible to use a specific solvent for the organic species. In the last case, however, the solution containing this species, must dissolve, at least partially, in the sol and has to be compatible with the gelation process. It is known that C6 0 shows very poor solubility in any solvent, except aromatic and especially halogenated aromatic solvents [13]. Among the possible solvents, we decided to use monochlorobenzene (MCB) because of its relatively low boiling point (132 °C). In order to check the possibility to deposit films with a sol-gel solution containing MCB, we prepared a sol with molar ratios of tetraethoxysilane (TEOS)/H 2 0/HCl/EtOH/MCB = 1/2/0.01/6/3.5. Using the fresh s
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