ABSORPTION AND EMISSION PROPERTIES OF A 2-CATENAND, ITS PROTONATED FORMS, AND ITS COMPLEXES WITH LI- TUNING OF THE LUMINESCENCE OVER THE WHOLE VISIBLE SPECTRAL REGION(, CU+, AG+, CO2+, NI2+, ZN2+, PD2+ AND CD2+ )

The absorption spectra (at 298 K), luminescence spectra and lifetimes (at 77 and 298 K) and luminescence quantum yields (at 298 K) of a cate nand, its mono- and diprotonated forms, and its complexes with Li+, Cu +, Ag+, CO2+, Ni2+, Zn2+, Pd2+ and Cd2+ in CH2Cl2 solutions are obtain ed. The catenand (L) consists of two interlocked 30-membered rings, ea ch one containing a 2,9-diphenyl-1,10-phenanthroline-type co-ordinatin g moiety. Upon addition of trifluoroacetic acid to CH2Cl2 solutions of L, significant changes in the absorption and luminescence properties are observed, that are fully reversed on addition of base. Comparison with the behaviour of a reference compound, 2,9-di(p-methoxyphenyl)-1, 10-phenanthroline suggests that the catenand protonation does not occu r at each phenanthroline-type moiety, but involves co-ordination of bo th moieties around one or two protons (in HL+ or H-2L2+ respectively). The free catenand shows 1(pipi) fluorescence (lambda(max) = 400 nm, tau = 2.0 ns, PHI = 0.42) at 298 K, and both 1(pipi) fluorescence (la mbda(max) = 382 nm, tau = 2.2 ns) and 3(pipi) phosphorescence (lambda (max) = 524 nm, tau = 0.79 s) in a rigid matrix at 77 K. The metal com plexes of L are forced to have a tetrahedral-type co-ordination geomet ry because of the entwined arrangement of the two phenanthroline ligan ds. The only exception is for the Pd2+ complex in which orthometallati on is observed to avoid a tetrahedral co-ordination. The complexes wit h Li+, Cd+ and Zn2+ exhibit ligand-centred (l.c.) fluorescence and pho sphorescence, this being considerably more perturbed from that of L fo r the divalent ions. The complexes of Co2+ and Ni2+ are not luminescen t, as expected because of the presence of low energy metal-centred lev els which offer a pathway to a fast radiationless decay of the l.c. le vels. The copper(I) complex exhibits an emission band in the red spect ral region (298 K: lambda(max) = 730 nm, tau = 175 ns, PHI = 0.001 1; 77 K: lambda(max) = 690 nm, tau = 1.1 mus), that can be assigned to th e lowest energy triplet metal-to-ligand charge transfer (m.l.c.t.) exc ited state. For the silver(I) complex no emission can be observed at r oom temperature, whereas in a rigid matrix at 77 K a very intense, lon g-lived band is present at about 498 nm (tau = 0.01 2 s) that can be a ssigned to the lowest 3l.C. level. The palladium(II) complex, in which the first co-ordination sphere of the metal ion is constituted by C-- phenyl and two phenanthroline nitrogens of a diphenylphenanthroline un it and a nitrogen of the other diphenylphenanthroline unit, displays a n emission band at 555 nm (tau = 3.0 x 10(-4) s) at 77 K that can be a ssigned to a perturbed 3m.l.c.t. level. The emission maxima of L, HLand H-2L2+ and its six luminescent metal complexes cover the range 378 -730 nm, showing that it is possible to tune the luminescence of the L derivatives over the whole visible spectral region.