Solvent-Dependent Stoichiometry in Perylene–7,7,8,8-Tetracyanoquinodimethane Charge Transfer Compound Single Crystals

Perylene forms three binary compounds with TCNQ. Using a physical vapor transport (PVT) method, mixtures of P1T1 (perylene1–TCNQ1), P2T1 (perylene2–TCNQ1), and P3T1 (perylene3–TCNQ1) crystals can be grown simultaneously. Solution-grown crystals exhibit a stoichiometry that depends on the solvent used and not on the initial stoichiometry of the perylene and TCNQ: only single crystals of P1T1 were grown from toluene, and only P3T1, from benzene. Precipitation–dissolution theory was employed to explain this phenomenon. We found that P1T1 is less soluble than P3T1 in toluene, which resulted in its preponderant growth from this solvent. Using the same argument, we could also explain the growth of P3T1 from benzene. Crystallization of P2T1 from solution was not possible. In addition, steady-state and time-resolved fluorescence measurements indicate that the difference in solubility of TCNQ in benzene and toluene leads to different fluorescence spectra due to selective crystallization of P1T1 and P3T1 from toluene and benzene.