A computational study of unique properties of pillar[n]quinones: Self‐assembly to tubular structures and potential applications as electron acceptors and anion recognizers

Abstract

Density functional theory has been used to calculate the thermodynamic properties and molecular orbitals of pillar[n]quinones. Pillar[n]quinones are expected to be effective electron acceptors and the ability to accept more than one electron increases with the size of the interior cavity. Pillar[5]quinone and pillar[7]quinone show a great intramolecular charge transfer upon the electron excitation from highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) as indicated by a large difference of electron distributions between their HOMO and LUMO and a notable dipole moment difference between the ground and first triplet excited state. The aggregation of pillar[n]quinones leads to tubular dimeric structures joined by 2n CH···O nonclassical hydrogen bonds (HBs) with binding energies about 2 kcal/mol per HB. The longitudinal extension of the supramolecular self-assembly of pillar[n]quinone may be adjustable through forming and breaking their HBs by controlling the surrounding environment. The tunability of the diameter of the tubular structures can be achieved by changing the number of quinone units in the pillar[n]quinone. The electrostatic potential maps of pillar[n]quinones indicate that the positive charge in the interior cavity decreases as the number of quinone units increases. Chloride and bromide anions are chosen to examine the noncovalent anion-π interactions between pillar[n]quinones and captured anions. The calculations show that the better compatibility of the effective radius of the anions with the interior dimension of pillar[n]quinone leads to larger stabilization energy. The selectivity of spatial matching and specific interaction of pillar[n]quinone is believed to possibly serve as a candidate for ionic and molecular recognition.

Recent Progress on Organic Electrodes Materials for Rechargeable Batteries and Supercapacitors

“…The cathode was another macrocyclic molecule, pillar[5]quinone (P5Q), containing five quinone units that are linked by methylene bridges at para positions [118,119,120], with a pillar architecture that is favorable to Li uptake. The pillar[5]quinone cathode in this all-solid-state battery with Li-anode and poly(methacrylate) (PMA)/poly(ethylene glycol) (PEG) electrolyte showed an average voltage of ∼2.6 V and a high initial capacity of 418 mAh g −1 , with 94.7% capacity retention after 50 cycles at 0.2C rate (89.2 mA g −1 ) through the reversible redox reactions of enolate/quinonid carbonyl groups.…”

Pillarquinones and Pillararenequinones

“…A DFT calculation of the whole series of pillar[n]quinones (n = 3-7) rendered electrostatic potential maps, which demonstrates that the internal cavities have positive charges which decrease with increasing numbers n. [7] Guests such as Cl À or Br À should be firmly complexed -particularly in the cavities of the smaller pillar[n]quinones.…”

Synthesis of Pillar[6]arenes and Their Host–Guest Complexes

“…A DFT study predicted interesting complexation properties for pillar [6]quinone as an anion sensor. 33…”

“…The charge transfer occurring in this complex can be directly observed by the appearance of a light red color (Scheme 17). 33,34 The K a value amounts in acetonitrile to (2.5 ± 0.2) × 10 5 M -1 and in acetone to (3.9 ± 0.1) × 10 5 M -1 .…”