Dimerization of Conjugated Radical Cations: An Emerging Non‐Covalent Interaction for Self‐Assembly

Abstract

Aromatic stacking has played a significant role in the design of discrete supramolecular systems. However, for many years, the stacking of conjugated radical cations has been considered only as a novelty due to its weakness. In recent years, it has been demonstrated that the stacking of conjugated radical cations, particularly those formed by bipyridinium or tetrathiafulvalene, can be enhanced remarkably when they are incorporated into rationally designed, preorganized frameworks or entrapped into a confined space. This Focus Review highlights the recent advance in its application as an emerging non-covalent force for the construction of various supramolecular structures.

Dynamic supramolecular polymers built from cucurbit[n]urils and viologens

“…From an electrochemical point of view, these dicationic compounds are subject to two consecutive Nernstian electron transfers attributed to the successive formation of the cation radical V +• and neutral quinonic forms V 0 . The growing interest for viologen derivatives in supramolecular chemistry over the past decades thus mainly stems from the acceptor properties of the dicationic V 2+ ‘ground’ state and from the stability of the radical cation state V +• which can both be implemented for the construction of supramolecular assemblies …”

“…The vast majority of π‐dimers reported so far in the literature involve intermolecular overlaps imposed either in the solid state by packing effects or favored in solution by the use of unusually high concentrations of radicals. To cope with this problem, one strategy which has proved quite effective in promoting the formation of noncovalent long‐bonded dimers in standard temperature and concentration ranges relies on the use of container molecules, such as the cyclodextrins or CB[ n ]s, capable of hosting and stabilizing such self‐assembled dimeric entities …”

Tuning the Energy Gap by Supramolecular Approaches: Towards Near‐Infrared Organic Assemblies and Materials

“…The radical dimers showed red‐shifted absorption in the NIR region, which are promising building blocks of NIR materials. Furthermore, other examples concerning the stabilization of radical dimers in confined environments exist, which have been reviewed by Zhang, Li, and co‐workers, mainly focused on viologen, tetrathiafulvalene and oligothiophene radical cations. Various novel NIR supramolecular assemblies and materials have been fabricated based on the dimerization of radicals, such as supramolecular polymers and two‐dimensional supramolecular organic frameworks.…”

Self‐Assembly of Azobenzene Derivatives into Organogels and Photoresponsive Liquid Crystals

“…[1][2][3][4][5][6] The controlo f weak and multiple noncovalent interactions, such as hydrogen bonding, p-p stacking, and van der Waals forces, at the molecular level, is critical in regulating the nano-to micro-size architectures, chromophore packing, and opticalp roperties. [11][12][13][14] Amongv arious molecular self-assemblies, p-organogels have become one of the most attractive soft materials, which have provedt ob ev aluable platforms in aw ide range of fields including fluorescence sensing, opto/electronic devices,etc. [11][12][13][14] Amongv arious molecular self-assemblies, p-organogels have become one of the most attractive soft materials, which have provedt ob ev aluable platforms in aw ide range of fields including fluorescence sensing, opto/electronic devices,etc.…”