SUPRAMOLECULAR PHOTOCHEMISTRY AND PHOTOPHYSICS - A [3]-CATENAND AND ITS MONONUCLEAR AND HOMODINUCLEAR AND HETERODINUCLEAR [3]-CATENATES

The absorption, emission, and excitation spectra and the luminescence quantum yields and lifetimes of the emitting excited states of a [3]-catenand and some of its metal complexes ([3]-catenates) have been investigated. The [3]-catenand (1) is made of a central 44-membered ring, carrying two 1,10-phenanthroline units, interlocked with two 30-membered rings each of which carries a 1,10-phenanthroline unit. In CH2Cl2 solution at 298 K, 1 exhibits a strong fluorescence band (lambda(max) = 404 nm, tau = 2.4 ns, Phi = 0.33) which at 77 K is accompanied by a phosphorescence band (lambda(max) = 519 nm, tau = 0.8 s). In the dicopper(I) catenate, CU2.1(2+), the ligand centered (LC) fluorescence and phosphorescence bands are completely quenched and emission takes place from a metal-to-ligand charge-transfer (MLCT) excited state (298 K: lambda max = 735 nm, tau 168 ns, Phi = 5.9 X 10(-4) 77 K: lambda(max) = 750 nm, tau = 1.4 mu s). In the monocopper(I) species Cu.1(+), which contains a catenand-type and a catenate-type moieties, the LC fluorescence of the former moiety is strongly quenched (tau = 40 ps) by the presence of the latter. In the Ag-2.1(2+) catenate, the LC fluorescence cannot be observed, but a strong LC phosphorescence is present at 77 K (lambda(max) = 502 nm, tau = 17 ms). Investigations have also been made on three heterodinuclear [3]-catenates, whose synthesis is fully described. In the heterodimetallic CuAg.1(2+) catenate only the MLCT emission of the Cu+-based moiety is present (298 K: lambda(max) = 735 nm, tau 162 ns, Phi = 6.1 X 10(-4); 77 K: lambda(max) = 735 nm, tau = 1.8 mu s). The CuZn.1(3+) catenate exhibits a weak and short-lived (90 ps) LC fluorescence from the Zn2+.based moiety accompanied by the MLCT emission of the Cu+-based one. For the CuCo.1(3+) catenate, no luminescence is observed, indicating that the potentially luminescent MLCT excited state of the Cu+-based moiety is quenched by the Co2+-based one. The quenching of the MLCT excited state of Cu.1(+), Cu-2.1(2+), CuAg.1(2+), and CuZn.1(3+) by oxygen and acetone has been investigated and photosensitization of singlet oxygen luminescence has been observed. The results obtained are discussed and compared with those previously reported for analogous [2]-catenates and knots.