Design And Assemblying Of Fluorescent Receptors For Molecular Recognition And Chemosensing

This thesis consists of five chapters.In Chapter One, the discovery and developments in the field of fluorescent sensing and molecular recognition were briefly reviewed. Examples include (1) important sensing mechanisms for metal ions, (2) design of recognition systems for saccharides, (3) recognition systems based on fast radiationless internal conversion (IC) and (4) fabrication and applications of self-assembled monolayers (SAMs). The research proposals of this dissertation were outlined.Recent r esearches h ave shown t hat a fast radiationless i nternal c onversion (IC) occurs in 1-dimethylaminonaphathalene (DMAN) via vibronic coupling of the proximate S1 and S2 states, in which S1 is the emissive state of intramolecular charge transfer (CT) character. We assumed that varying the energy of the emissive S1 by modifying DMAN molecular structure or varying solvent polarity could change energy gap AE (S1, S2) between S1 and S2 states, therefore modulating the IC. In Chapter Two, DMAN derivatives were synthesized to reveal how the electron donating ability of the N-substituent influences the internal conversion.Sodium 1-naphthylaminodiacetate (NADA) with two carboxylmethylene groups substituted at the amino nitrogen atom was synthesized and its fluorescence spectra in aqueous-organic binary solvents with organic components of methanol, ethanol, n-propanol, i -propanol, and a cetonitrile w ere i nvestigated. It w as o bserved t hat both the fluorescence intensity and quantum yield of NADA increased with increasing solvent polarity, suggesting that IC indeed occurred with NADA in aqueous-organic binary solvents. A decrease in the energy gap between S1 and S2 states was assumed for the enhanced internal conversion with NADA compared toDMAN.To further study the influence of N-substitution and solvent on the IC in 1-aminonaphthalene derivatives, we synthesized N-methyl-N-methoxycarbonyl methyl-1-aminonaphthalene (MMAN) and N, N-dimethoxycarbonylmethyl-1-amino naphthalene (DCAN) replacing N-CH3-substitents in DMAN by -CH2CO2CH3. Results were analyzed in terms of Weller theory by correlating the emission energy with the oxidation potentials of the electron donor within the investigated fluorophores. Meanwhile, the ground-state structures of DMAN derivatives were optimized with the aid of AMI calculations. The electron density of the nitrogen atom coincides well with the electrochemistry results which indicate that the amino groups in MMAN and DC AN had obviously lower donating ability that accounted for the enhanced IC. Substitution of -CH2CO2CH3 on the amino group increases the dihedral angle between the amino and naphthyl plane moiety, which was supported by the observation of the blue-shift of the absorption maximum of DCAN and MMAN in organic solvents relative to that of DMAN and the 1H NMR data of the chemical shifts of proton at C-2 of the MMAN and DCAN that are at lower field than that of DMAN. It was therefore concluded that the IC could be modulated by either modulation of the electron donating/accepting ability by N-substitution or solvatochromic effect.Because of the impact of the intramolecular charge transfer (ICT) on the IC process, we decided to develop a molecule recognition and fluorescence sensing system of DMAN-like hosts. For this purpose, 2-(l-naphthyl)aminoacetic acid (NAA), sodium 1-naphthylaminodiacetate (NADA) and N-(l-naphthyl)-N', N'-carboxymethylethylenediamine (NCEA) were designed based on the chelating ability to a variety of metal ions of the well-known chelator, ethylenediamine tetraacetic acid (EDTA).In Chapte three, we investigated the fluorescence spectra of NAA in aqueous solution in the presence of Cu2+, Co2+, Ni2+ and Zn2+, and found that the fluorescence of NAA was quenched by these transition metal ions to differentextents, of which the quenching by Cu2+ was substantially higher than those of the other metal ions of similar electronic structure, which did not completely followed the order of the stability constants of the metal-NAA complexes. Further...