Series of charge transfer complexes obtained as crystals in a confined environment

A series of charge transfer complexes (CTCs) were successfully formed by solvent free processing techniques, using the 1,2,4,5-tetracyano benzene (TCNB) as piA molecule and a series of p-dihydroquinones (H2Qs) as piD counterparts. Additionally to the classical co-evaporation techniques, we obtained CTCs in less than an hour, in a very simple confined environment, between two 100 mu m - spaced glass plates. A systematical study by Raman spectroscopy on crystals highlighted the CTCs formation. Moreover, three new crystalline structures were obtained, namely TCNB-H2Q that crystallizes in columns connected to each other by H-bonds, while with the methoxy- and dimethoxy-H2Qs the CTC forms crystals with the stoichiometry 1 : 2, TCNB-(H2QOMe)2 and TCNB-(H2QOMe2)2. In TCNB-(H2QOMe)2 layers are formed due to intermolecular hydrogen bonds, while in TCNB-(H2QOMe2)2 molecules arrange in triads, with piA-piD interactions. In all cases, strong piA-piD interactions exist with intermolecular distances lower than the van der Waals distances, which results in strong absorption bands in the visible range.