Chemical crosslinking in C60 thin films

Abstract

Various procedures have been developed for the modification of fullerene films (Karachevtsev et al. 2002; Käsmaier et al. 1996; Li et al. 2003; Rao et al. 1993; Rhee et al. 2003; Talyzin et al. 2002; Yogo et al. 2002; Zhao et al. 1994). During the last decade, there has been a great interest to polymerise C60 fullerene films on various substrates, photopolymerisation being one of the most common methods. This interest was stimulated with great potential technological possibilities of polymerised fullerene films. The photopolymerisation changes the solubility of fullerene films, and influences their physical and chemical characteristics (Käsmaier et al. 1996; Li and Pittman, 2003; Zhokhavets et al. 2003). On the other hand, photoirradiation induces not only the fullerene polymerisation, but also the formation of other carbonaceous phases (Käsmaier et al. 1996). Thus, finding an alternative way is highly desirable. Among the whole rich chemistry of fullerenes, their interactions with amines gained a special attention (Adamov and Vojinovic-Miloradov, 1998; Bernstein and Foote, 1999; Dresselhaus et al. 1993; Goh et al. 2000; Hirsch et al. 1991; Lobach et al. 1995; Nigam et al. 1995; Qiao et al. 2000a,b; Schick et al. 1995; Wudl et al. 1992). A direct addition reaction of amines onto C60 molecules was discovered more than a decade ago (Hirsch et al. 1991; Wudl et al. 1992). Both primary and secondary amines (which are all neutral nucleophiles) add onto C60 at room temperature by reacting with fullerene dissolved in liquid amines or in their solutions in dimethylformamide, dimethylsulfoxide, chlorobenzene, etc. (Goh et al. 2000; Hirsch et al. 1991; Nigam et al. 1995; Schick et al. 1995; Wudl et al. 1992). The reaction stoichiometry varies significantly depending on the size of amine molecule. For smaller amine molecules such as 2-methylaziridine, the average amine:C60 ratio can reach as much as 10:1 (Nigam et al. 1995). Recently we described a solvent-free reaction of silica-supported C 60 with vaporous nonylamine at 150°C, which produces a mixture of addition products as well (Basiuk et al. 2003). According to C:N ratio found from elemental analysis, the average number of nonylamine molecules attached to C60 is 3. Nevertheless, field-desorption mass spectrometric study detected a series of molecular and fragment ions due to the adducts with up to six nonylamine moieties chemically bound to C60. In the present paper, we tested applicability of the gas-phase technique to the reaction of fullerene C60 thin film with 1,8-diaminooctane (or 1,8-octanediamine), a representative of long-chain aliphatic diamines, which can be expected to react with two or more neighbour fullerene molecules simultaneously and thus to act as a cross-linking agent (Fig. 20.1). Our main interest was in the preparation of relatively insoluble C60 films, which can be similar to the photopolymerised fullerene films in their stability, but at the same time the undesirable formation of other carbonaceous phases would be avoided. © Springer-Verlag Berlin Heidelberg 2006.