Ab initio and semi-empirical calculations on a supramolecular structure consisting of the electron acceptor molecule bianthrone covalently linked to the electron donor molecule 2,3-dimethyl-6-alkyl-1,4-dithiafulven are prensented. The molecule may act as a molecular switch and calculations show that a charge transfer state is involved in the initial stage of the switch process. The charge recombination process is calculated to occur early in the switching process. Experimental data supports this interpretation and calculations are used as a guideline for synthetic strategies leading to molecules with improved switching properties.