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MM4.01 - Multiple Stoichiometries in Organic Single Crystals of Charge Transfer Compound 
April 8, 2015   8:00am - 8:15am

Single crystals of organic charge transfer compounds with low concentration of imperfections and high purity are outstanding objects for the study of relation between charge transfer and physical properties. The degree of charge transfer in compounds impacts antiferromagnetism, superconductivity, electron-phonon interactions and energy storage. Crystal growth of binary compounds made from organic donors and acceptors is more complicated than that of monomolecular crystals. For studies of charge transfer degree, compounds with multiple stoichiometries are especially desired. However, systems with multiple stoichiometries are rare. Due to the different physical properties (solubilities, sublimation temperatures) of donors and acceptors, the stoichiometry of the synthesized compounds may differ from the stoichiometry of the starting materials. In this study we observed an interesting phenomenon: the final stoichiometries of single crystal P1T1 (perylene1:TCNQ1) and P3T1 (perylene3:TCNQ1) are not affected by the stoichiometry of the starting materials, but by the solvent in which the perylene-TCNQ crystals were grown. The P1T1 crystals were grown from toluene, whereas the P3T1 crystals were grown from benzene regardless of the acceptor/donor stoichiometry in the starting materials. The solubility data were employed to analyse the effect of solvent on the stoichiometry of the perylene-TCNQ charge transfer single crystals. Steady-state optical spectra and time-resolved fluorescence measured in a mixture of perylene and TCNQ in toluene and benzene, confirmed selective crystallization of P1T1 and P3T1 from toluene and benzene. In contrast to solution growth, when utilizing the physical vapour transport (PVT) method, a mixture of monomolecular crystals, P1T1 (perylene1:TCNQ1), P2T1 (perylene2:TCNQ1) and P3T1 (perylene3:TCNQ1) is obtained. P2T1 is a new discovered structure. The charge transfer degrees of P1T1, P2T1 and P3T1 have been measured and calculated. Field-effect transistors on the single crystals� surfaces of P1T1, P2T1 and P3T1have been made. The results reveal thatP1T1 is typically an n-type semiconductor, P3T1 showed p type behaviour, whereas P2T1 showed ambipolar properties.

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