Efficient Intermolecular Charge Transport in π-Stacked Pyridinium Dimers Using Cucurbit[8]uril Supramolecular Complexes

Abstract

Intermolecular charge transport through π-conjugated molecules plays an essential role in biochemical redox processes and energy storage applications. In this work, we observe highly efficient intermolecular charge transport upon dimerization of pyridinium molecules in the cavity of a synthetic host (cucurbit[8]­uril, CB[8]). Stable, homoternary complexes are formed between pyridinium molecules and CB[8] with high binding affinity, resulting in an offset stacked geometry of two pyridiniums inside the host cavity. The charge transport properties of free and dimerized pyridiniums are characterized using a scanning tunneling microscope-break junction (STM-BJ) technique. Our results show that π-stacked pyridinium dimers exhibit comparable molecular conductance to isolated, single pyridinium molecules, despite a longer transport pathway and a switch from intra- to intermolecular charge transport. Control experiments using a CB[8] homologue (cucurbit[7]­uril, CB[7]) show that the synthetic host primarily serves to facilitate dimer formation and plays a minimal role on molecular conductance. Molecular modeling using density functional theory (DFT) reveals that pyridinium molecules are planarized upon dimerization inside the host cavity, which facilitates charge transport. In addition, the π-stacked pyridinium dimers possess large intermolecular LUMO–LUMO couplings, leading to enhanced intermolecular charge transport. Overall, this work demonstrates that supramolecular assembly can be used to control intermolecular charge transport in π-stacked molecules.

Enhanced π–π Stacking between Dipole-Bearing Single Molecules Revealed by Conductance Measurement

“…The slightly larger twist angle of AZ1 is potentially due to the stronger steric repulsion between the larger seven-membered ring and the adjacent phenyl ring. Although the difference in twist angles is moderate, according to previous studies, the slightly larger twist angle in AZ1 does not account for our observations because it should theoretically weaken π–π stacking , and suppress molecular conductance. , In contrast, we observed stronger π–π stacking and higher conductance for monomers and dimers of AZ1 than NA1, which is in the opposite trend of the twist angle effect.…”

Molecular Engineering of Noncovalent Dimerization

“…Despite the deep dive in solutions and solid states, dimerization at the interface is important yet rarely explored, particularly in pseudostatic systems. Recent attempts of using noncovalent dimers as single-(supra)­molecular circuits have provided valuable information on charge transport , and quantum interference . With a complexation nature that is neither fast exchanging nor completely static, it is anticipated that pseudostatic chromophore dimers at the interface would be robust yet self-adaptive tectons or linkers for the fabrication of optical molecular devices.…”

Bioinspired Design of an Uncharged Ambipolar Helical Scaffold To Achieve Efficient Solid‐State Proton Conduction

“…[12,13] Proton transport through discrete organic solids is being actively pursued with an aim of creating conductive organic scaffolds. [14][15][16][17][18] Various interactions that aided in creating such scaffolds include π-π stacking, [19][20][21][22][23][24] H-bonding with charged species [25][26][27][28][29] and by generating covalent/hydrogen bonded crosslinked frameworks that incorporate charged proton carriers such as NH 4…”

“…Proton transport through discrete organic solids is being actively pursued with an aim of creating conductive organic scaffolds [14–18] . Various interactions that aided in creating such scaffolds include π‐π stacking, [19–24] H‐bonding with charged species [25–29] and by generating covalent/hydrogen bonded crosslinked frameworks that incorporate charged proton carriers such as NH 4 + , H 3 O + , H 2 SO 4 , HCl and ionizable acidic functionalities such as −SO 3 H, −COOH, −PO 3 H 2 to boost the inherently poor conductivity of organic molecules [30–36] . However, these ionic residues may also be prone to degradation by hydrolysis or dissolution, especially under the high humidity and elevated temperature conditions required for achieving high conductivity in these systems.…”