Lattice instability coupled with charge and/or spin degrees of freedom has become an significant area of research in solid state science as the electric, magnetic and optical properties exhibit high susceptibility to external stimuli. Typical examples of π-conjugated molecular solids are charge-transfer (CT) complexes that have 1D stacks of alternating π-electron donor (D) and acceptor (A) molecules. Here, we explore the tiling of electron deficient macrocycles (Naphthalene-diimide triangle, NDI-Δ) and electron donor (tetrathiafulvalene, TTF) for the design of two or three-dimensional organic conductors and photo-conductors. Previous studies have shown that the tris-radical NDI-Δ3-* behaves as a spin frustrated system with a ferromagnetic ordering at 20K. While studies on the monoradical NDI-Δ-* revealed that the electron is shared between the three NDI units and theoretical bandgap calculations suggested that it has a metallic ground state at room temperature. The packing of the NDI-Δ in the crystal structure is very sensitive to solvent. While in chlorinated solvents - CHCl3 and CH2Cl2 - NDI-Δ crystalizes in the cubic P213 and I213 space groups without forming p…p interactions between the NDI units, crystallization from MeCN leads to the tiling of the NDI-Δ through close π…π interactions between the NDI units (triclinic P1 space group). Co-crystallisation of the NDI-Δ with TTF is, as well, very sensitive to solvent identity. Three sets of cocrystals have been obtained from MeCN, CHCl3 and CH2Cl2, named respectively CT-C, CT-B and CT-C (Figure 1). Solvent modulation plays a critical role in controlling not only the D/A stoichiometry ratio and the molecular arrangement in the crystal structure, but it also prevents the inclusion of the guest (TTF) inside the cavity of the NDI-Δ macrocycle. This behavior has a direct impact on the electronic properties of these composites. While inclusion of TTF inside the cavity in CT-A complex enhances the electron transfer to generate a ionic phase with semiconductive properties, CT-B and CT-C complexes are neutral. Crystallographic, spectroscopic, electron transport and magnetic studies has been undertaken to unravel the physical properties of the different NDI-Δ and TTF CT complexes.

Supramolecular triangular tiling of electron active macrocycles for the design of organic conductors and photoconductors

2019 Spring National Meeting

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