New Charge Transfer Cocrystals of F2TCNQ with Polycyclic Aromatic Hydrocarbons: Acceptor–Acceptor Interactions and Their Contribution to Supramolecular Arrangement and Charge Transfer

Abstract

A series of new charge-transfer cocrystals of F2TCNQ with anthracene, tetracene, and chrysene was prepared and characterized. The donor and acceptor molecules are arranged in alternating D–A–D–A stacks. The linear acenes in combination with F2TCNQ form layered structures due to in-plane lateral donor–acceptor and acceptor–acceptor interactions via multiple C–H···N and C–H···F hydrogen bonds, which govern the crystal structure and significantly alter face-to-face π–π interactions. In the cocrystal of F2TCNQ with chrysene no interactions between acceptor molecules are observed, and the π–π interactions prevail. Thus, the donor–acceptor interplanar distance is the smallest in the chrysene complex despite its lower energy level of the HOMO and weaker donor ability, as determined through electrochemical oxidation potentials in this series of PAHs. The charge-transfer values estimated through empirical correlations and QTAIM analysis also do not manifest a direct dependence on the donor ability of PAHs. Thus, though face-to-face π–π interactions dictate the formation of cocrystals, the lateral noncovalent interactions are as important for the supramolecular arrangement and charge transfer. UV/vis spectroscopy and electronic structure quantum chemical calculations show that these cocrystals may be classified as small-gap semiconductors with energy gaps of 0.7–1.3 eV.