Quinoxaline−Imidazolium Receptors for Unique Sensing of Pyrophosphate and Acetate by Charge Transfer

Abstract

Quinoxaline derivatives (1−4) bearing two imidazolium moieties are found to strongly bind anions and show unique charge-transfer fluorescent responses to pyrophosphate and acetate, whereas they show excimer formation with other anions. Anion-binding studies are investigated with fluorescence and 1 H NMR analysis, single-crystal X-ray analysis, and theoretical calculations.Anions play a fundamental role in a wide range of chemical and biological processes, and numerous efforts have been devoted to the development of abiotic receptors for anionic species. 1 Sensors based on anion-induced changes in fluorescence 2 and intramolecular/intermolecular excimer formation 3 appear to be particularly attractive. On the other hand, given that carboxylic acids (or carboxylates) are a common functional group in biological and synthetic organic molecules, the development of simple to sophisticated receptors for carboxylates has attracted immense attention. 4 The imidazolium group can make a strong interaction with anions through the (C-H) + -X --type ionic hydrogen bond-ing involving the dominating charge-charge electrostatic interaction 5 which is in contrast to well-known neutral receptors involving typical hydrogen bonding for the anion

Recognition and sensing of anions through synergistic effects using simple benzimidazolium-urea receptors

“…The angle C8-H8A···Cl1 is 126.04°, suggesting the ionic − hydrogen bond is weaker than that observed other receptors [61,62]. Moreover, the crystal structure reveals that the chloride anion forms strong hydrogen bonds with two urea protons (H3B, and H4C), as well as forming a hydrogen bond with a proton of the aromatic benzene ring (H4A).…”

Understanding Clusters toward the Design of Functional Molecules and Nanomaterials

“…Various receptors showing either cation recognition [158][159][160][161][162] or anion recognition [163][164][165][166][167][168][169][170][171][172][173][174][175][176][177][178][179][180] have been synthesized and charcterized in the past decades. Despite these achievements, further research efforts are required to address the issues related to the selective recognition of anion/cation in real life samples for the environmental and biological use.…”

“…Thus, utilization of such ionic hydrogen bonding improves the binding affinity for the anion. Based on ab initio calculations, highly selective imidazolium-based anionophores have been designed [171][172][173][174][175][176][177][178][179][180] and synthesized. Imidazolium tripodal receptor 3 (Fig.…”

“…179 The rapid charge transfer in the excited state was observed from the quinoxaline moiety to the deprotonated imidazolium moiety as the binding with pyrophosphate/acetate formed a deprotonated complex where the imidazolium hydrogen transferred to pyrophosphate/acetate.…”

Selective “naked-eye” sensing of acetate ion based on conformational flexible amide-pyridinium receptor

“…The rate of AcO -production and oxidation has been frequently used as an indicator of organic decomposition in marine sediments [12]. However, until now, selective chromogenic and/or fluorescent sensors for AcOare quite limited [9,[13][14][15][16], compared with a large number of reported sensors for F -and H 2 PO 4 -, which have similar basicity to AcO -. Most of the AcO -sensors usually also display response to H 2 PO 4 -and F -, especially the latter [7,[17][18][19][20].…”