| Abstract
| - Novel gallium cofacial anthracene-bridged diporphyrins have been prepared and fully characterized. The X-ray structure for (DPA)[Ga(OMe)]2, (DPA)[Ga−(OH)−Ru(CO)], and (DPA)[Ga(OMe)−Ru(MeOH)(CO)] porphyrins have also been obtained. The luminescence properties are reported and are characterized by weak ππ* fluorescences (2 < τF< 7 ns) arising from the low energy Q-bands (S1→S0) of the gallium porphyrins. In all cases, the phosphorescence is either quenched or very weak.
- The preparation and characterization of a new series of mixed metal cofacial anthracene-bridged diporphyrins(DPA) containing a GaL fragment (L = OMe, OH) and another metallic center (M = GaL, Ru(CO)(OH), Co,and H2 (i.e. free base)) are reported. The luminescence properties at 298 and 77 K, in degassed EtOH solution,are also reported, and are characterized by a weak ππ* fluorescence (2 < τF< 7 ns) arising from the low energyQ-bands (S1→S0). In the mixed diporphyrin systems, a strong ππ* fluorescence is detected from the free base,while the transition metalloporphyrins of Co(II) and Ru(II) do not emit. The homobimetallic di[Ga(OMe)] speciesexhibits an unprecedented double ππ* fluorescence arising from the two lowest energy absorption Q-bands. Onthe basis of a comparison with photophysical data on GaL monoporphyrins, the weak fluorescence and absenceof phosphorescence for most cases indicate efficient intramolecular quenching. To define structural features, theX-ray structures of (DPA)[Ga(OMe)]2 (2), (DPA)[Ga−(OH)−Ru(CO)] (5a), and (DPA)[Ga(OMe)−Ru(MeOH)(CO)] (5b) have been obtained. The structures of 5a and 5b demonstrate an interesting aspect of the structuralchemistry of these ligands related to the internal methoxide and methanolic ligands in 5b (resulting in a largeinterplanar separation and center-to-center distance) and the internal metal-bridging hydroxyl ligand in 5a (resultingin a small interplanar separation and center-to-center distance). These data support previously reported discussionson the ability of the DPA and the DPB analogue (diporphyrinylbiphenylenyl) ligands to open and close their“bite” around the binding pocket between the porphyrin macrocycles.
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