Derivatized polymers provide a versatile platform for creating multifunctional assemblies. 1 This includes polypyridyl complexes of Ru II and Os II which have high absorptivities in the visible based on metal-to-ligand charge transfer (MLCT) transitions. 2,3 An early synthetic strategy for these involved attachment to polystyrene by an ether linkage (I). We have developed a new strategy based on amide linkage (II) 3 and find that there is a dramatic difference between the two in their ability to promote intrastrand energy transfer.The amide polymer was prepared from a 1:1 styrene-paminomethylstyrene copolymer of polydispersity 1.5 and an average of 16 repeat units. 3 The amide link was formed by reaction with the acid-derivatized complexes, [M II b 2 b-COOH]-(PF 6 ) 2 (M ) Ru, Os; b ) 2,2′-bipyridine (bpy), b-COOH ) 4′-methyl-2,2′-bipyridine-4-carboxylic acid) by using standard amide coupling conditions (see the Supporting Information). 3 The resulting homopolymer samples are distributions, on the average, containing 16 complexes and abbreviated as [co-PS-CH 2 NHCO-(M II 16 )](PF 6 ) 32 (M ) Ru, Os). A mixed polymer was prepared by sequential coupling, first to the Os II complex in limited amount (in a ratio of 3:16 relative to available anine sites on the polymer) with isolation and purification and then with the Ru II complex in excess. This gave a polymer of average composition [co-PS-CH 2 NHCO-(Ru II 13 Os II 3 )](PF 6 ) 32 (1). The derivatized polymers were purified and characterized by 1 H NMR, IR, UV-vis, and electrochemical measurements, as described previously. 3,4 For example, for mixed polymer 1, waves for the Ru III/II and Os III/II couples appear at 1.30 and 0.87 V vs SCE in CH 3 CN 0.1 M in [N(n-C 4 H 9 ) 4 ](PF 6 ) having the expected relative peak currents of 13:3.Transient resonance Raman measurements on an ether-linked model complex, [Ru II b 2 b-CH 2 OBz](PF 6 ) 2 (b-CH 2 OBz is 4-CH 2 -OBz-4′-CH 3 bpy, Bz is benzyl) in acetonitrile, show that bpy is the acceptor ligand in the lowest MLCT excited state. 5 Transient resonance Raman measurements (Supporting Information) on model complexes for the amide, [Ru II b 2 b-CONHBz](PF 6 ) 2 (b-CONHBz is 4-CONHBZ-4′-CH 3 bpy), [Ru II (b-CONHBz) 3 ]-(PF 6 ) 2 , [Ru II b 3 ](PF 6 ) 2 , and the polymer [co-PS-CH 2 NHCO-(Ru II 16 )](PF 6 ) 32 in acetonitrile reveal that the acceptor ligand is the bpy-amide. This is shown by the appearance of resonantly enhanced bands for b-CONH-radical anion in the region cm -1 with 368.9 nm excitation and scattering (the superscript "a" denotes bands which overlap with neutral ligand bands). On the basis of structure II and the results of molecular modeling, 4 this means that the excitedstate dipole is aligned along the amide ligand oriented toward the polymer backbone and nearest neighbor complexes.In the ether-linked polymer, [co-PS-CH 2 OCH 2 -(Ru II 22 Os II 5 )]-(PF 6 ) 54 (2), energy transfer from Ru II * to Os II is favored by 0.36 eV and occurs rapidly with k > 2 × 10 8 s -1 (τ < 5 ns) in acetonitrile solution at ...
