Connecting molecule oxidation to single crystal structural and charge transport properties in rubrene derivatives

Abstract

The study of a series of rubrene derivatives appropriately designed for limiting oxidation can be a powerful tool for clarifying the role of oxidation in the transport properties of crystalline rubrene, which is still unclear. Here, the synthesis of a series of substituted rubrene derivatives from dimerisation of propargyl alcohols is described together with the analysis of their stability to oxidation and electrochemical properties in solution. Millimetre-sized single crystals of all derivatives are grown and their structure determined from single crystal X-ray diffraction, which shows for all of them crystal packing features closely resembling those of orthorhombic rubrene. Finally, charge transport is studied by means of conductive AFM. The comparison between charge conduction in the crystalline state, oxidation potentials, and photo-oxidation kinetics allows ruling out rubrene endoperoxide as the origin of the high charge conductivity in both rubrene and rubrene derivatives, in agreement with an oxygen-enhanced conductivity model.