Analysis of 'H NMR spectra (400 MHz) revealed a novel mode of interaction between cyclodextrin (CD) and carbazoleviologen linked compounds (CACnV), where the spacer chain was consisted of n methylene units ( n = 4,6, 8, 10, and 12). In the case of a-CD, the complexed species lived long enough to afford distinct proton signals, when the spacer chain was relatively long (n 1 8). As to CAClZV, the equilibrium constant for the 1:l complex was 4.9 X lo4 M-' at 30 OC and coalescence temperatures for the proton signals exceeded 100 OC. Clear NOES were observed to prove strong interaction between the protons in the CD cavity and the spacer methylene groups of CAC12V. The spacer was concluded to be encased in the cavity of a-CD. In the case of d-CD, essentially the same "through-ring CD complex" was formed. The line shape analysis indicated that the free energies of activation at 70 OC for complexation and decomplexation were 11.6 and 17.2 kcal/mol, respectively. Activation parameters for the a-CD complexes were evaluated by the rate of disappearance of intramolecular charge-transfer absorption (420 nm) on the addition of a-CD. The free energy of activation for decomplexation was found to exceed 22 kcal/mol in the a-CD complexes for CACnV (n = 8, 10, and 12). The viologen moiety of CACnV was concluded to be the site of entrance for forming "through-ring CD complex", and the large activation energies were ascribed to dehydration of viologen units to go through the CD cavity.

α,ω-Alkanedicarboxylic acid anions with a long spacer methylene chain were observed to form dynamically and statically stable complexes with α-cyclodextrin (α-CD) at an NMR time scale in both neutral and basic media. The structures of these complexes were confirmed to be a “through-ring” type CD complex by measurements of the intermolecular NOESY and NOE difference spectra. From the thermodynamic data in basic media (pD 13), the dynamical stability of these type complexes were attributed not to the steric interaction, but to an electrostatic interaction between the dicarboxylate anion and ionized-CD.

Modified electrodes were fabricated by depositing a monolayer containing porphyrin-viologen linked compound on ITO electrodes by Langmuir-Blodgett method. Visible light irradiation on the modified electrodes afforded stable anodic photocurrents. The photocurrents clearly increased in the presence of magnetic fields. The magnetic field effects on photocurrents, as observed for the first time, are ascribed to the contribution of triplet radical pairs.

No abstract

On the addition of α-cyclodextrin (CD), an intramolecular charge-transfer absorption band of an anthracene-viologen linked compound rapidly disappeared with elapsed time. The reason was ascribed to formation of a through-ring CD complex, which hinders direct interaction between the donor- and acceptor moieties. Thermodynamic parameters, including the energy of activation for complexation of α-CD, were evaluated by the use of the charge-transfer absorption band in D2O- and H2O solutions. Solvent deuterium isotope effects were observed with the free energy change on complexation, but not with the energy of activation for formation of the through-ring CD complex. An open, extended conformer of the linked compound was proposed as the model of the activated state for forming the through-ring CD complex.