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A gold nanoparticle surface-modified with amide ligands shows enhanced optical sensing of anions: the detection limit is increased by about three orders of magnitude higher than that originally expected from the anion binding ability of neutral amide ligands.

The evaluation of the dediazoniation kinetics of various m-and p-substituted benzenediazonium tetrafluoroborates' in 1,2-dichloroethane at 50" in the presence of 18-crown-6, 2 1-crown-7 and dicyclohexano-24-crown-8 demonstrates that the rate constant for the dediazoniation within the complex (k2) is smallest, and the equilibrium constant for complex formation (K) is largest for the complexes with 21-crown-7 (cf Scheme 1). The logarithms of the equilibrium constants ( K ) for complex formation with each of the crown ethers studied correlate well with Hammetf's substituent constants, D , to give reaction constants p= 1.18-1.38.A linear correlation between the logarithms of the rate constants for the dediazoniation within the complex with those of the dediazoniation rate constants of uncomplexed diazonium ions (log k2 vs. log. k l ) , found for most substituted diazoniurn salts, indicates that the dediazoniation mechanism of the complexed diazonium ions is not significantly different from that of the free ions. For very electrophilic diazonium ions (p-Cl, rn-CN), k2 was much larger than expected on the basis of the linear log k2 vs. log k , relationship. Analysis of the dediazoniation products showed that this was due to a change in mechanism from heterolytic to homolytic dediazoniation.The complexation rate of diazonium salts by crown ethers (k,) is practically diffusion controlled and does not change much with the size of the crown ether. The decornplexation rate ( k d ) , however, is significantly lower for complexes with 2 1crown-7, than for those with 18-crown-6 and dicyclohexano-24-crown-8, and is therefore the reason for the variations in the equilibrium constant ( K ) and thus for the fact that complexes of arenediazonium salts with 21-crown-7 are the most stable.The amounts of the N,-NB rearrangement, as well as those of the exchange of the I5N-labelled diazonio group with external nitrogen during dediazoniation of p-toluenediazonium salt were independent of the addition of crown ethers. ') Part xx: see [I].

Novel heterocyclic quinol-type fluorophores (4 a-c) and (5 a-c) that contain substituents (R = Me, Bu, Ph) with nonconjugated linkages to the chromophore skeleton have been synthesized and their photophysical properties have been investigated in solution and in the solid state. Considerable differences in the absorption and fluorescence spectra were observed between the two states. Quinols 4 a-c and 5 a-c exhibited almost the same absorption and fluorescence spectra in solution; however, their solid-state fluorescence excitation and emission spectra in the crystalline state were quite different. We performed X-ray crystallographic analyses to elucidate the dramatic effect of the substituents of the nonconjugated linkage on the solid-state fluorescence excitation and emission spectra. The relationships between the solid-state photophysical properties and the chemical and crystal structures of 4 a-c and 5 a-c are discussed on the basis of the X-ray crystal structures.

Novel indeno[1,2-b]benzo[4,5-e]pyran-11-one-type fluorophores exhibiting intense solid-state fluorescence were conveniently synthesized and the relation between their solid-state photophysical properties and the X-ray crystal structures were investigated, which demonstrates that non-planar structures with sterical hindered substituents prevent the fluorophores from forming short pi-pi contacts causing fluorescence quenching in the solid state.

The crystals of the title fluorescent clathrand exhibit a drastic fluorescence enhancement behavior upon contact with carboxylic acid vapors. The magnitude of the fluorescence change is greatly dependent on the enclathrated carboxylic acid molecules and increase in the following order: formic acid < acetic acid < propionic acid. To elucidate the enclathrated guest effects on the fluorescence properties of the crystals, the X-ray crystal structures have been determined.

An isomeric pair of novel imidazoanthraquinol fluorophores 2 and 3 exhibiting two tautomeric forms (A and B) that are possible for the imidazole ring have been developed. In order to control the tautomeric form to improve the fluorescence properties, the N-butylated imidazole derivatives 6 and 7 have further been synthesized. The fluorescence intensity of the quinols was in the order 3 { 6 o 7 o 2 in benzene, which is quite different from the order 3 { 2 { 6 o 7 in the crystalline state. To investigate the effect of N-alkylation of imidazole ring on the photophysical properties of the quinol fluorophores in solution and in the crystalline state, we have performed semi-empirical molecular orbital calculations (AM1 and INDO/S) and X-ray crystallographic analysis. On the basis of the results of calculations and the X-ray crystal structures, the N-alkylation effects on the chemical structure of the quinol fluorophores and on their solid-state photophysical properties are discussed. w Part 3. For Part 2, see: ref. 4b. z Electronic supplementary information (ESI) available: Table S1 Crystal data and structure refinement parameter for the quinol derivatives 2a, 3a, 6 and 7. See