Tipping the Balance with the Aid of Stoichiometry: Room Temperature Phosphorescence versus Fluorescence in Organic Cocrystals

The interaction of the co-former 1,4-diiodotetrafluorobenzene (I2F4) with the conjugated hydrocarbons diphenylacetylene (DPA) and trans-trans-stilbene (tS) leads to formation of the novel co-crystals DPAI2F4 (1), DPA(I2F4) 2 (2), tSI2F4 (3), and tS(I2F4) 2 (4).These materials have been synthesized by mechanochemical methods and characterized by X-ray techniques and luminescence spectroscopy in the solid state.In the co-crystals, the DPA and tS molecules interact with the molecules of I2F4 via halogen bonds (XB) of the kind halogen•••phenyl (Hlg•••π).As a result of the external heavy atom effect, and depending on the stoichiometry, these co-crystals exhibit both fluorescence and phosphorescence (1 and 3) or exclusive phosphorescence (2 and 4) at room temperature.Differences in the luminescence efficiencies between the DPA-and tS-containing materials are observed.