The cation complexation force of 18-crown-6 has been measured in ethanol by means of atomic force microscopy using probe tips and mica substrates modified chemically with 18-crown-6 and ammonium ion, respectively. The specific complexation force was suppressed by free potassium ion in the measurement solution, indicating a blocking effect based on the competitive complexation of the 18-crown-6 moiety between the free ion and the ammonium ion bound to the substrate. The single complexation force of 18-crown-6 with ammonium ion was evaluated to be about 60 pN in ethanol by autocorrelation analyses of the histograms for observed forces.

Tuning of localized surface plasmon resonance (LSPR) of metal nanostructures has attracted a great deal of interest, and the controlled syntheses of them have been extensively studied for fine tuning of their LSPR. In this paper, we report widely tunable LSPR from visible to near-infrared of hollow silver nanoshells synthesized by reduction of silver thiocyanate. The silver nanoshell exhibits size- and thickness-dependent LSPR for symmetric dipole mode from visible to near-infrared regions, while the antisymmetric dipole resonance is not changed. By combining characterization of the nanoshells by transmission electron microscopy and theoretical simulation based on discrete dipole approximation, we reveal that the LSPRs are controlled by the size and shell thickness of the nanoshells and also that dimples on the shell surfaces would significantly affect the LSPRs of symmetric dipole, and quadrupole mode for larger nanoshells.

Received 20th March 2000, Accepted 7th April 2000 Published on the Web 22nd May 2000Metal-ion complexation of crown ether derivatives incorporating one and two spirobenzopyran units was investigated by electrospray ionization mass spectrometry. The crowned spirobenzopyran derivatives exhibited very different metal ioncomplexing behavior from their corresponding parent crown ether rings, preferring multivalent to monovalent metal ions owing to the additional ionic interaction with the nitrophenolate anion of the merocyanine moiety. The on-line photochemical reaction for mass spectrometry indicated that the metal ion-complexing ability and ion selectivities of the crowned spirobenzopyrans can be switched photochemically, taking advantage of the difference between the spiropyran and merocyanine isomers.

We have measured the single intermolecular force of a typical photoionizable molecule, spirobenzopyran, by means of atomic force microscopy, which has proven to be useful in measuring directly single molecular forces. The spirobenzopyran moiety was immobilized covalently on both Au-coated probe tips and substrates by use of a self-assembled monolayer of a hexanethiol derivative incorporating a terminal spirobenzopyran moiety, 1'-(6'-mercaptohexyl)-3',3'-dimethylindolino-6-nitrospiro-(2H-1-benzopyran-2,2'-indoline). Force curve measurements were carried out using the spirobenzopyran-modified probe tip and substrate under dark conditions and in situ UV light irradiation. The adhesion force observed in a polar solvent (i.e., ethanol) was increased substantially under in situ UV light irradiation, which caused photoisomerization of the spirobenzopyran moiety bound to both tip and substrate from its electrically neutral spiropyran form to the corresponding zwitterionic merocyanine one. Statistical analyses of the observed force by autocorrelation technique have revealed that the photoionization enhanced by UV light caused a remarkable increase in the single intermolecular force of the photochromic compound.

We have synthesised an inverse opal hydrogel functionalised with a thiourea moiety as an anion recognition site. The resulting hydrogel showed remarkable changes of its structural colour with respect to acetate and bicarbonate ions selectively in aqueous solution, indicating a potential as colorimetric sensing materials for hydrophilic anions.