Cyclophane fluorescence emission quenching

Water-soluble cyclophane 86145 exhibited a well-defined fluorescence band at 290 nm with a 210 nm excitation. The emission intensity was markedly increased by complexation with Zn2+ which forms a 2 1 (metal-ligand) complex. The fluorescence emission is pH-independent to pH 2. The fluorescence enhancement factor is 5.0 at pH 6 and 50 at pH 8.6 (due to the pH dependence of the free ligand). Ni2+ and Cu2+ ions quenched the ligand fluorescence via a PET mechanism. Furthermore, when cyclophane 86 was coordinated to Cu2+, the molar absorptivity of the transition band observed at 260 nm was increased by a factor of about 10. Such a large spectral change was not observed for the Zn2+ and Ni2+ complexes. In the Cu2+ complex, the two phenyl rings of the cyclophane are expected to be... 

Additionally, Hunter and coworker presented another model for the noncovalently linked donor-acceptor complex which was made up of triad components, quinone-cyclophane-porphyrin 144. H NMR measurements indicated the formation of a ternary complex and the association constant of BQ via hydrogen bonds was determined to be 1.4 x 10 M, while the association constant of pyridine of the cyclophane and zinc porphyrin was 3.2 X lO M in dichloromethane. The fluorescence emission from the zinc porphyrin in the presence of the cyclophane was clearly quenched by the addition of BQ, compared with a control experiment, due to diffusional quenching. This evidence indicated that the intracomplex ET occurred within the triad system. 

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