An Antenna Polymer for Visible Energy Transfer

Abstract

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 ...

Mimicking the antenna-electron transfer properties of photosynthesis

“…We (23)(24)(25)(26)(27)(28) and others (29 -32) have used derivatized polymers to gain insight into various aspects of the photosynthetic process. Recently, we showed, for example, that polymeric assemblies derivatized with polypyridyl complexes of Ru II and Os II display antenna and energy transport properties similar to natural photosynthetic systems (48,49). In the present work, we describe an assembly that combines both the light-harvesting and electrontransfer properties of a natural photosynthetic system within a single macromolecule.…”

Influence of pH on the Photochemical and Electrochemical Reduction of the Dinuclear Ruthenium Complex, [(phen)2Ru(tatpp)Ru(phen)2]Cl4, in Water: Proton‐Coupled Sequential and Concerted Multi‐Electron Reduction

“…(7)] and neutral or acidic conditions (pH 7) favoring a protoncoupled bielectronic process [Eq. (8)]. [43,44] P þ e À Ð P À ð5Þ…”

“…Additionally, some HP À may be the product of H 2 P losing a proton in solution. At pH 6, the first two reductions are no longer distinct, but instead, have merged to form a single two-proton, two-electron wave at À0.05 V (see Figure 3c), ultimately corresponding to the reaction given in Equation (8).…”

Driving Multi-electron Reactions with Photons: Dinuclear Ruthenium Complexes Capable of Stepwise and Concerted Multi-electron Reduction

“…These complexes have very high absorption coefficients in the visible region, are chemically robust and are capable of either energy transfer to other sites or direct charge-separation upon photoexcitation. In particular, significant advances have been made in the use of such complexes in antenna assemblies (Treadway et al 1997;Hissler et al 1999;Campagna et al 2002;Armaroli 2003;McClenaghan et al 2003;Baranoff et al 2004;Johansson et al 2004)for efficient energy transfer to a specific site and in dyad or triad assemblies (Scandola et al 1992;Dupray et al 1997;Campagna et al 2002;Morales et al 2002; to maximize either the CS state lifetime or distance of charge separation or both.…”