Supramolecular Photochemistry and Photophysics. A [3]-Catenand and Its Mononuclear and Homo- 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 CH2Cl2solution at 298 K, 1 exhibits a strong fluorescence band (λmax= 404 nm, τ = 2.4 ns, Φ = 0.33) which at 77 K is accompanied by a phosphorescence band (λmax= 519 nm, τ = 0.8 s). In the dicopper(I) catenate, Cu2·12+, 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: λmax= 735 nm, τ = 168 ns, Φ = 5.9 × 10-4; 77 K: λmax= 750 nm, τ = 1.4 μs). 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 (τ = 40 ps) by the presence of the latter. In the Ag2·12+catenate, the LC fluorescence cannot be observed, but a strong LC phosphorescence is present at 77 K (λmax= 502 nm, τ = 17 ms). Investigations have also been made on three heterodinuclear [3]-catenates, whose synthesis is fully described. In the heterodimetallic CuAg·l2+catenate only the MLCT emission of the Cu+-based moiety is present (298 K: λmax= 735 nm, τ = 162 ns, Φ = 6.1 × 10-4; 77 K: λmax= 735 nm, τ = 1.8 μs). The CuZn·13+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·13+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+, Cu2·12+, CuAg·12+, and CuZn·13+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.