Inverted thermochemistry of norbornadiene-quadricyclane molecular system inside fullerene nanocages

Currently, endofullerenes become common compounds that enrich chemistry by novel opportunities for molecular engineering. The influence of the fullerene cages on the behavior of guest molecules is obvious and not limited to simple encaging. Unfortunately, its quantitative estimation is difficult but this information may provide insights into regulating reactions by encapsulation. In the present work, we have applied the accurate DFT techniques to elucidate how encapsulation into the fullerene cages changes thermodynamic parameters and polarizability of norbornadiene <-> quadricyclane interconversion (a classic example of molecular systems for solar energy accumulation). As it is turned out, decreasing the size of the cage enhances thermodynamic favorability of the norbornadiene conversion. Moreover, when appropriately encapsulating, the primarily endothermic direct reaction becomes exothermic. This also holds true in the case of inorganic (boron-nitrogen) fullerenes with rigid structures. Thus, the found regularity is a general trend and encapsulation can be recommended as one of the ways to tune thermodynamic parameters of chemical reactions. (C) 2014 Elsevier B.V. All rights reserved.