Charge Delocalization in Self-Assembled Mixed-Valence Aromatic Cation Radicals

Abstract

The spontaneous assembly of aromatic cation radicals (D(+•)) with their neutral counterpart (D) affords dimer cation radicals (D(2)(+•)). The intermolecular dimeric cation radicals are readily characterized by the appearance of an intervalence charge-resonance transition in the NIR region of their electronic spectra and by ESR spectroscopy. The X-ray crystal structure analysis and DFT calculations of a representative dimer cation radical (i.e., the octamethylbiphenylene dimer cation radical) have established that a hole (or single positive charge) is completely delocalized over both aromatic moieties. The energetics and the geometrical considerations for the formation of dimer cation radicals is deliberated with the aid of a series of cyclophane-like bichromophoric donors with drastically varied interplanar angles between the cofacially arranged aryl moieties. X-ray crystallography of a number of mixed-valence cation radicals derived from monochromophoric benzenoid donors established that they generally assemble in 1D stacks in the solid state. However, the use of polychromophoric intervalence cation radicals, where a single charge is effectively delocalized among all of the chromophores, can lead to higher-order assemblies with potential applications in long-range charge transport. As a proof of concept, we show that a single charge in the cation radical of a triptycene derivative is evenly distributed on all three benzenoid rings and this triptycene cation radical forms a 2D electronically coupled assembly, as established by X-ray crystallography.

Synthesis and Electronic Properties of Triperyleno[3.3.3]Propellanes: Towards Two‐Dimensional Electronic Structures

“…Their unique molecular configuration have found application in various functional areas, for instance, as molecular motors and as ligands . Furthermore, chemical modification such as π‐fusion or substituent introduction on triptycene or trinaphtho[3.3.3]propellane (TNP, 1 , Scheme ), induces a strong π‐π interaction between molecules, leading to two‐dimensional (2D) molecular assemblies . In addition to their geometrical uniqueness, homoconjugation among three arenes have been active subjects of investigation due to the importance for both fundamental science and application in organic semiconductors such as OFET and photovoltaics.…”

Unraveling the Coulombic Forces in Electronically Decoupled Bichromophoric Systems during Two Successive Electron Transfers

“…structure B in Figure 1), and the accompanying spectrals ignature [4] signifying hole delocalization. structure B in Figure 1), and the accompanying spectrals ignature [4] signifying hole delocalization.…”

“…Cyclic voltamogramms (CVs) of hexaphenylbenzene-based polychromophoric molecules in CH 2 Cl 2 (0.2 m nBu 4 N + PF 6 À )atn = 100 mV s À1 (A) and 25-400mVs À1 (B and C)at2 28C. [4,5] The Coulombic interactions are known to scale inverselyw ith the distance between ap air of charges, however,b ased on examples B and C,o ne cannot discernt he critical distance at which the Coulombic forces will trigger.M oreover,i nA one cannot easily disentangle the relative contribution of Coulombic forces between closely juxtoposed charged chromophores in the presence of the inherentinterchromophoric electronic coupling. [4,5] The Coulombic interactions are known to scale inverselyw ith the distance between ap air of charges, however,b ased on examples B and C,o ne cannot discernt he critical distance at which the Coulombic forces will trigger.M oreover,i nA one cannot easily disentangle the relative contribution of Coulombic forces between closely juxtoposed charged chromophores in the presence of the inherentinterchromophoric electronic coupling.…”

Electron transfer pathways in mixed‐valence paracyclophane‐bridged bis‐triarylamine radical cations

“…Electron‐transfer (ET) processes in organic materials may occur intra‐ or intermolecularly. For the latter case, transmission of charge across stacks of π‐conjugated systems is of central interest . These processes are more difficult to analyze, both experimentally and quantum‐chemically, than intramolecular ones, e.g., those within a conjugated dye, as they depend crucially on the potentially flexible intermolecular structural arrangements and dynamics.…”