Crystal Growth, HOMO–LUMO Engineering, and Charge Transfer Degree in Perylene-F_xTCNQ (x = 1, 2, 4) Organic Charge Transfer Binary Compounds

The methodologies of searching for novel organic charge transfer binary compounds and large-size crystal growth, in the case that only the two starting organic substances are known but the phase diagram is not known, the thermodynamic data of the binary compound are not known, and even the existence of new binary compounds is not known, were studied. Centimeter-long crystals of novel perylene-F 1 TCNQ, perylene-F 2 TCNQ, and perylene-F 4 TCNQ charge transfer binary compounds are obtained from the gas phase. Kinetically lowering the sublimation rate is the key factor for growing large-size charge transfer compound single crystals. Changing the number of fluorine atoms in F x TCNQ results in the variation of the electron affinity, which further changes the HOMO–LUMO of acceptor. Charge transfer degree is increased with increasing of fluorine atoms in the perylene-F x TCNQ system. Therefore, the structure, stoichiometry, and kind of donor and acceptor enable HOMO–LUMO engineering of the charge transfer compound and tune the physical properties.