Design And Synthesis Of Thiourea-and N-Aminothiourea-Based Neutral Receptors For Anion Recognition

Molecular recognition is an important research area in supramolecular chemistry. The development of anion coordination chemistry is delayed compared with neutral molecules and cations. It is therefore necessary to construct novel anion receptors. In this thesis, we constructed intamolecular charge transfer (ICT) fluorescence ionophores based on proton coupled electron transfer (PCET) model and chromophores with ground-state ICT. Several highly selective and sensitive sensors for anions were developed.This dissertation consists of five chapters.In Chapter 1, researches in the development of anion recognition were briefly reviewed. The coordination chemistry of anions has received little attention over the last 30 years when compared to that devoted to coordination chemistry of cations. The development of anion sensors, however, becomes a of current attention, mainly because of the understanding that anions play key roles in biology, medicine, catalysis and environmental sciences. Therefore a number of anion recognition systems have been reported. The content of this chapter includes. (1) structural characters of anions, (2) noncovalent interactions existed in anion coordination, (3) electrochemical recognition of anions, and (4) optical sensing of anions. The research proposal of this dissertation was presented according to the developments of anion recognition researches.Chapter 2 describes synthesis and characterization by IR and 1H NMR of the ca.40 receptors designed in this thesis for sensing for anions. These receptors include N-(p-dimethylaminobenzoyl)thiourea derivatives, N-(p-dimethylaminobenzamido)-N'-phenylthiourea derivatives,N-(p-nitrophenyl)-N'-phenylthiourea derivatives, N-(p-nitroanilino)-N '-phenylthiourea derivatives, N-(p-nitroanilino)-N'-phenylurea derivatives, and bi(N-phenyl)thiourea derivatives.Anion recognition based on proton-coupled electron transfer (PCET) is established in thethird Chapter. We constructed fluorescent receptors for anions using p-dimethylaminobenzamide fluorescence that emits dual fluorescence as the optical-signaling unit convalently attached to anion recognition site such as thiourea. Three kinds of receptors were designed and synthesized, these are p-dimethylaminobenzamide (DMABA), N-(p-dimethylaminobenzoyl)thiourea (DMABTU), N-(p-dimethylaminobenzamido)-N'-phenylthiourea (DMABATUB). The new ICT fluorescent receptors were found to undergo sensitive response to the presence of several anions such as AcO-, -F, H2PO4-, HSO4-, C1O4-, NO3-, Cl-0 and Br- in acetonitrile and chloroform. This response was assumed to result from a proton coupled electron transfer within the formed 1:1 anion-receptor complex. As the dual fluorescence intensity ratio can be employed as sensing index in ratiometric assays, the sensing is much less subject to fluctuation in excitation source that is suffered in total fluorescence intensity sensing mode.The intramolecular charge transfer dual fluorescence of DMABA in acetonitrile was found to show highly sensitive response to HSO4 over several other anions such as H2POO4-. AcO- and C104-. The dual fluorescence intensity ratio and total intensity of DMABA decreased while the dual fluorescence position remained unchanged in the presence of bisulfate. A Stern-Volmer quenching behavior was found and the quenching constant Ksv was 2.03 X 104 mol-1 L for HSO4-. Absorption titration indicated that a 1:1 complex formed between HSO4- and DMABA, which gave a binding constant of 2.02 X 104 mol-1 L. In acetonitrile solution of DMABA and HS04-mixture addition of methanol or ethanol led to the recovery of the absorption spectrum of DMABA, which supports the hydrogen-bonding nature for the interaction between DMABA and HSO4-. The hydrogen-bonding interaction between HSO4- and DMABA was further probed by NMR titration in DMSO-d6 that indicated a downfield shift of the NMR signal of NH proton of DMABA in the presence of HSO4-. The obvious isotopic effect observed in the fluorescence quenching [Ksv(HSO4-)/Ksv(DSO4-)= 1.63] suggested that...