Synthesis of Molecular Receptors and Applications in Host-Guest Interaction and Molecular Recognition

Abstract

Supramolecular chemistry, based on non-covalent interactions, has been developed for decades since the discovery of crown-ether. Upon close understanding of the essence of binding events between hosts and guests, numerous synthetic molecular and ion receptors come into being. Molecular recognition is the most important branch of supramolecular chemistry, and researchers are stilling taking efforts to design and produce more efficient and costless chemosensors. In chapter 2, simplest compounds having 2n-crown-n topology (n = 3): trioxane scaffold based hosts were synthesized and characterized by 1H NMR, crystallography and theoretical calculation. These neutral hosts could bind anions through pure aliphatic C–H (Cali–H) hydrogen bonding (HB) in benzene and/or acetonitrile via C–H bonds strongly polarized by two adjacent oxygen atoms in this scaffold as well as electron-withdrawing substituents. This work will give rise to the development of trioxane based anion receptors and introduce selectivity by altering the substituent shape and electronic property. In chapter 3, bis-imidazolium based host [3-1]2+ were synthesized. X-ray structures of [3-1]Cl2 and another reported organic crystal BUXTOD in which a chloride anion bound exclusively by multiple hydrophobic Cali–H groups were reported. The Cali–H•••Aˉ interactions are driven by the formation of a near-spherical electron density distribution structure around the anion with +/- alternating layers of electrostatic charge. Instead of strong HBs, weak Cali–H HB-like donors are more readily to form such near-spherical patterns. In chapter 4, a novel carbazole based two photon fluorescence probe MPVC-I was designed and synthesized. MPVC-I was able to selectively monitor carbon monoxide in air by palladium catalyzed azidocarbonylation, reaching a capability of detecting 50 ppm CO in air within 30 min at 90 °C. Reaction process was confirmed by liquid chromatography combined with mass spectroscopy. In chapter 5, conjugated carbazole based turn-on fluorescence probe P1 was designed, synthesized and found to be selective for strong oxidizing agent hypochlorite and permanganate. P1 responded hypochlorite with a rate constant of 0.00588 min-1 while for permanganate, 0.0522 min-1. The simplest oxidation mechanism based on only proton and electron transfers was determined, and the reducing capability of the probe could be tailored by controlling the conjugation length.