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

Density functional theory has been used to calculate the thermodynamic properties and molecular orbitals of pillarn]quinones. Pillarn]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. Pillar5]quinone and pillar7]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 pillarn]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 pillarn]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 pillarn]quinone. The electrostatic potential maps of pillarn]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 pillarn]quinones and captured anions. The calculations show that the better compatibility of the effective radius of the anions with the interior dimension of pillarn]quinone leads to larger stabilization energy. The selectivity of spatial matching and specific interaction of pillarn]quinone is believed to possibly serve as a candidate for ionic and molecular recognition. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011