Tetrathiafulvalene-Based Macrocycles Formed by Radical Cation Dimerization: The Role of Intramolecular Hydrogen Bonding and Solvent

Compounds 1 a and 1 b were prepared by appending two tetrathiafulvalene (TTF) units to an aromatic amide segment that is driven by six or two intramolecular NH⋅⋅⋅O hydrogen bonds to adopt a folded conformation. UV/Vis absorption experiments revealed that if the TTF units were oxidized to TTF.+ radical cations, the two compounds could form a stable single molecular noncovalent macrocycle in less polar dichloromethane or dichloroethane or a bimolecular noncovalent macrocycle in a binary mixture of dichloromethane with a more polar solvent owing to remarkably enhanced dimerization of the TTF.+ units. The stability of the (TTF.+)2 dimer was evaluated through UV/Vis absorption, electron paramagnetic resonance, and cyclic voltammetry experiments and also by comparing the results with those of control compound 2. The results showed that introduction of the intramolecular hydrogen bonds played a crucial role in promoting the stability of the (TTF.+)2 dimer and thus the noncovalent macrocyclization of the two backbones in both uni‐ and bimolecular manners. A dime(rization) a dozen: Inherently weak dimerization of tetrathiafulvalene (TTF) radical cations can be strengthened remarkably if two TTF units are attached to a hydrogen‐bonding‐driven aromatic amide foldamer segment and oxidized to TTF⋅+. The dimerization can lead to the formation of a uni‐ or bimolecular noncovalent macrocycle, depending on the polarity of the solvent.