Linkers that tether donors and acceptors can greatly impact electron/energy transfer processes and are important in designing artificial photosynthetic systems. Work to be presented focuses on studying the impact of side chain change of different oligopeptide linkers (e.g. aminoethyglycine (gly), aminoethyvaline (val), aminoethyleucine (leu) and aminoethyphenylalanine (phe) ) on the emission photodynamics of a series of [Ru(bpy)3]2+-[M(bpy)2]2+ complexes (M = Cu, Pd or Zn). Photophysical data of the dimetallic complexes shows for all the Ru-Cu complexes the radiative decay rates are similar but the non-radiative decay rate decreases as the steric bulk of the side chain increases. A similar trend was observed for the Ru-Pd complexes. Temperature dependent non-radiative decay rates for all the Ru-M complexes were obtained to probe the activation energies of the non-radiative decay processes. For all the Ru-Cu complexes, Ru-phe-Cu has the highest activation energy, which agrees with the smallest non-radiative decay rate; the barrier decreases as the side chain gets smaller. In the Ru-Pd complexes, the same trend was observed. In all cases, no trend was observed for the Ru-Zn complexes. Solvent study shows all the Ru-Cu and Ru-Pd complexes have a negative trend of non-radiative decay rates vs. Pekar factor but no trend was observed for the Ru-Zn complexes. Together these observations lead to our hypothesis that Ru-Cu and Ru-Pd have an electron transfer non-radiative decay mechanism and is different from the mechanism of Ru-Zn. The impact of side chain change on the non-radiative decay of Ru-Cu and Ru-Pd is probably due to (a) the conformation change to accommodate more sterically-hindered functional groups, which changes the donor-acceptor distance; and (b) the change of local dielectric by the side chains. Our modular and extendable supramolecular system is a good model for studying soft linkages between donors and acceptors.

Impact of side chain substituents on the emission photodynamics of [Ru(bpy)3]2+ with artificial oligopeptide linked [Cu(bpy)2]2+, Pd[(bpy)2]2+ or [Zn(bpy)2]2+

248th National Meeting (2014)

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