PHOTOPHYSICS OF METAL-ORGANIC PI-CONJUGATED POLYMERS

A series of polyaryleneethynylene pi-conjugated polymers that contain fac-(5,5'-diethynyl-2,2'-bipyridine)Re-I(CO)(3)Cl as part of the pi-co njugated polymer backbone have been synthesized by Pd-mediated couplin g chemistry. Three metal-organic polymers P10, P25 and P50, have been prepared which contain, respectively, 10, 25 and 50 mol.% of the Re(I) repeat units in the polymer chain. These polymers have been character ized by H-1- and C-13-NMR and FTIR spectroscopy and gel permeation chr omatography. The analysis indicate that the pholymers contain the inta ct Re(I) chromophore and M-n values of 10-15 kDa are typical (GPC, rel ative to polystyrene). The metal-organic polymers feature two spectral ly-distinct absorption bands, one due to the pi, pi absorption of the polymer backbone and another at lower energy which is attributed to t he d pi (Re)-->pi(poly) metal to ligand charge transfer (MLCT) absorp tion. The luminescence properties of the polymers have been examined i n fluid solution at 298 K and in a 2-methyltetrahedrofuran (MTHF) solv ent glass at 77 K. These spectroscopic studies reveal that: (1) fluore scence from the (1) pi, pi exciton state is observed at 2.80 eV in al l of the polymers at 298 and 77 K, but the intensity and lifetime of t he fluorescence is quenched as the mole fraction of Re in the polymers increases; (2) phosphorescence from the (3) pi, pi state of the conj ugated polymer backbone is observed at 1.93 eV in P10-P50 at 77 K; (3) luminescence from the d pi-->pi MLCT state is observed at 1.8 eV in the metal-organic polymers at 77 K. (C) 1998 Elsevier Science S.A.