COMPLEXES CONTAINING 2,9-BIS(P-BIPHENYLYL)-1,10-PHENANTHROLINE UNITS INCORPORATED INTO A 56-MEMBERED RING - SYNTHESIS, ELECTROCHEMISTRY, AND PHOTOPHYSICAL PROPERTIES

We synthesized a new macrocycle (1) which is made of a 56-membered rin g and contains two 2,9-bis(p-biphenylyl)-1,10-phenanthroline ligands. Then we prepared the complexes [Cu(1)(2)](+) (a catenate species), [Cu (3)(2)](+), [Cu(2)(3)](+) (a threaded species), Re(1)(CO)(3)Cl, and Re (3)(CO)(3)Cl, where 2 is a 33-membered macrocycle containing a 2,9-di- p-phenyl-1,10-phenanthroline ligand and 3 is an acyclic ligand contain ing the same 2,9-bis(p-biphenylyl)-1,10-phenanthroline unit which is p resent in 1. The absorption spectra of the free ligands in CH2-Cl-2 so lution show very intense bands in the near-UV region, characteristic o f their aromatic moieties. In the Cu(I) complexes, besides the perturb ed ligand-centered bands, weak metal-to-ligand charge-transfer (MLCT) bands can be observed in the 400-700 nm region. In the Re(I) complexes the MLCT bands lie at higher energy because the oxidation potential o f Re(I) is much more positive than that of Cu(I). At room temperature, ligands 1 and 3, which contain an extensively conjugated aromatic uni t, show a very strong (Phi = 0.89), short-lived (1.7 ns) fluorescence band with lambda(max) = 419 nm. The fluorescence of 2 is blue shifted (lambda(max) = 387 nm) and less intense (Phi = 0.29) because of the le ss extended conjugation and rigidity of its chromophoric unit. Besides fluorescence, also a long-lived (second time scale) phosphorescence i s displayed by the three ligands in a rigid matrix at 77 K. At room te mperature the [Cu(1)(2)](+), [Cu(3)(2)](+), and [Cu(2)(3)](+) species exhibit a weak (Phi similar to 10(-3)), relatively long-lived (10(2) n s time scale) emission with lambda(max) around 750 nm, which can be as signed to a triplet metal-to-ligand charge-transfer ((MLCT)-M-3) excit ed state. This emission is slightly red shifted and considerably longe r lived (tau similar to 2 mu s) at 77 K. The Re(1)(CO)(3)Cl and Re(3)( CO)(3)Cl complexes at room temperature show a moderately weak (Phi sim ilar to 10(-2)), long-lived (10(2) ns time scale) (MLCT)-M-3 emission with lambda(max) around 610 nm. At 77 K this emission is blue shifted (lambda(max) = 560 nm) and considerably longer lived (tau similar to 1 0 mu s). In the [Cu(1)(2)]+ catenate and in the Re(1)(CO)(3)Cl complex one of the two chelating sites of the macrocycle 1 is coordinated to the metal and the other one is free. Besides a (MLCT)-M-3 emission, th ese species exhibit the fluorescence band of the 2,9-bis(p-biphenylyl) -1,10-phenanthroline unit, strongly quenched by the nearby metal-based chromophoric unit (k(q) = 1.6 x 10(10) and 1.4 x 10(10) s(-1) for the Cu(I) and the Re(I) complex, respectively). In aerated solution all o f the complexes sensitize the (1) Delta(g)(O-2) luminescence at 1269 n m.