Ionochromic effects and structures of metalated poly(p-phenylenevinylene) polymers incorporating 2,2 '-bipyridines

The effects of metal ion chelation to the 2,2'-bipyridine (bpy) groups on t he photophysics and exciton dynamics of two conjugated polymers 1 and 2 in solution are investigated. The structures of polymers 1 and 2 have 2,2'-bip yridyl-5-vinylene units that alternate with one and three 2,5-bis(n-decylox y)-1,4-phenylenevinylene monomer units, respectively. The photophysics and exciton dynamics of metalated polymers 1 and 2 are compared to those of the metal-free polymers (Chen ct al. J. Phys. Chem. A 1999, 103, 4341-4351). T he origins of ionochromic effects due the metal ion chelation were studied using both steady-state and transient optical spectroscopy, and the results indicate that both conformational flattening and participation of Jr elect rons from the metal in the pi-conjugation of the polymer backbone play impo rtant roles in metal ion binding induced red shifts in absorption and photo luminescence spectra. The photoluminescence properties of the metalated pol ymers are determined by the metal ion electronic structures, where the clos ed shell Zn2+-bound polymer 2 has an increased photolumincscence quantum yi eld and the corresponding open shell Ni2+- or Fe3+-bound polymers have quen ched photoluminesccnce due to spin-orbit coupling. The dual character of me talated polymer 2 as a conjugated polymer and as a metal-bpy complex is dis cussed. In addition, the structures of metal ion binding sites are studied via X-ray absorption fine structure (XAFS) and are related to the photophys ical properties of the metalated polymers.