On the dependence of electronic properties on geometric structure for cubane derivatives and oligomers with donor and acceptor groups Elena Konstantinova * , Paulo M.V.B. Barone, Sócrates O. Dantas Departamento de Física, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, MG, Brazil article info Article history: Received 9 November 2008 Received in revised form 22 May 2009 Accepted 2 June 2009 Available online 7 June 2009 Keywords: Cubane Cubatriene Oligomers DFT Electronic properties abstract We report on the theoretical investigation of some structural and electronic properties for several fam- ilies of cubane-based compounds. All these compounds consist on cubane building blocks with electron donor and acceptor groups linked to molecular structure in different positions, with different numbers of double bonds and also saturated and unsaturated oligomers. Our calculations show that the increase of the number of double bonds leads to the decrease of the energy gap, simultaneously with the increase of the heat of formation. This property also depends of the number and positions of the double bonds in the compounds. According to our simulations, the electron transfer from the donor group to the acceptor group is a typical phenomenon in the cubane compounds. Therefore, the cubane or cubatriene based olig- omers with the NH 2 and NO 2 groups can be regarded as perspective materials to be used as nano-size push–pull systems. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Since the first synthesis [1], cubane was a subject of active re- search. Cubane has one of the most interesting and unusual struc- tures among all carbon molecules. Its C–C–C bond angle is 90° and this feature defines some special properties of this molecule and its derivatives. The geometrical structure of cubane is illustrated in Fig. 1 where R 1 –R 8 are hydrogen atoms. Recently there has been discovered a new efficient methodology for the synthesis of differ- ent kinds of substituted cubanes [2–5]. These cubane structures consist of a single cubane block linked to various groups of atoms, including the groups NH 2 and NO 2 [6–8]. Therefore, cubane and substituted cubane can be used to synthesize chains of several lengths (oligomers) [6,9]. The substitution of hydrogen atoms gives rise to atomic sites which can be used as reactive paths or to con- trol electronic properties of the resulting compounds, while side groups can provide charge injection or depletion on the molecular structure. These effects are potentially interesting for designing molecular devices which include cubane molecules as constituents [10–12]. Recently, there were numerous works devoted to the the- oretical investigations of carbon based structures which contain electron donor and acceptor groups [13–18]. Some of these studies were using the ab initio methods [13–17] through different kinds of computational software, while in some cases the investigations were based on the efficient combination of the DFT and semi- empirical methods [18]. One of the most interesting aspects of the cubane compounds with the donor and acceptor groups is the possibility of an electron transfer within the compound. We can state that the cubane-based materials possess some remark- able properties and hence are potentially useful for technological applications, as discussed in [19,20]. In this respect it looks important to perform an extensive theo- retical investigation of the electronic and structural properties of cubane compounds. In the present work we consider electronic properties of cubanes and its derivatives, in particular the cubanes containing electron donor and acceptor groups in different posi- tions associated to the cubic structure (see Fig. 1 and Table 1) and also saturated and unsaturated oligomers of these compounds (see Figs. 2 and 3, respectively). Our purpose is the systematic anal- ysis of the electronic properties of a cubane molecule, depending on the positions of the links (connection points) between the elec- tron donor and acceptor groups and the cubane compound and on the number of double bonds. Furthermore, we investigate the elec- tronic properties of oligomers consisting from the cubane and cub- atriene blocks with the groups NH 2 and NO 2 at the ends of the chains. Finally, we explore the possibility of the transfer of the in- ter-molecular charge. It turns out that the electronic dislocation in the molecular structure of the cubane and its derivatives (satu- rated and unsaturated) and oligomers enables one to use this com- pounds as a ‘‘bridge” between the donor and acceptor groups. 2. Methodology The illustration of the molecular structures under consideration is presented in Fig. 1 and the detailed exposition of the necessary 0166-1280/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.theochem.2009.06.001 * Corresponding author. Tel.: +55 32 3217 4707; fax: +55 32 3229 3312. E-mail address: konst@fisica.ufjf.br (E. Konstantinova). Journal of Molecular Structure: THEOCHEM 909 (2009) 116–121 Contents lists available at ScienceDirect Journal of Molecular Structure: THEOCHEM journal homepage: www.elsevier.com/locate/theochem