Novel ferrocene-modified artificial nucleobase receptors were designed and synthesized. The nucleobase receptors possess hydrogen-bonding and pi-stacking interaction sites that act simultaneously for binding to 1-butylthymine utilizing the pivot character of the ferrocene skeleton. Diamidopyridine was chosen for the hydrogen-bonding moiety, and various polynuclear aromatics were used for pi-stacking one. The two components were tethered to the cyclopentadienyl rings via ethynediyl and oxymethylene spacers. The binding affinity of the receptors to 1-butylthymine was found to be dependent on the aromatic structures. Thus, the association constants for perylene-linked receptors were approximately doubled compared to those of aromatic-free ones, an energy difference of approximately 0.5 kcal/mol. Detailed comparisons between the 10 receptors clarified the value of the pivot character of the ferrocene for construction of the intermolecular interaction site.
Novel unsymmetrical squarylium dyes which absorb in the near-infrared region were synthesized by a stepwise procedure via intermediate 4-substituted 3-hydroxycyclobut-3-ene-1,2-diones. By introducing benz[c,d]indoline or benzo[b]pyran moieties at one end as an electron-donating component, the SQ dyes exhibited their absorption maxima at 739-821 nm with large molar absorption coefficients (log ε = 4.96-5.18) in CHCl 3 . The X-ray analysis for one of these dyes was also examined to confirm the overall structure of the unsymmetrical SQ dye.
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