Thermal and photoinduced electron transfer in directional Bis(terpyridine)ruthenium(II)-(Bipyridine)platinum(II) complexes

Abstract

Metalloligands L1 and L2 consisting of directional bis(terpyridine) ruthenium(II) units and bipyridine moieties were constructed by amide formation. From these metalloligands two Ru-Pt heterobimetallic complexes 1 and 2 were derived by a building-block method by means of platination with [PtCl 2(dmso)2]. Both bimetallic complexes 1 and 2 feature metal-to-ligand charge transfer (MLCT) absorptions, and emission occurs at room temperature in fluid solution from 3MLCT(Ru) states in all cases. Energy transfer from platinum to ruthenium is observed in 2 but not in 1 (light harvesting). The one-electron-reduced species [1]- and [2] - were prepared by reduction of 1 and 2 with decamethylcobaltocene. EPR spectra and DFT calculations reveal that the spin density is localized at the tpy-CO/Ru (tpy = terpyridine) site in [1]-, whereas it is centered at bpy-CO/Pt (bpy = 2,2′-bipyridine) in [2]-. Efficient photoinduced electron transfer from triethanolamine to 1 and 2 is feasible by excitation at 500 nm [MLCT(Ru)]. Heterobimetallic complexes Pt-Ru (1) and Ru-Pt (2) were constructed from directional bis(terpyridine) ruthenium(II) and bipyridinedichloroplatinum(II) moieties. The photophysical properties of 1 and 2 as well as their responses to one-electron reduction (thermal and photochemical) were elucidated by EPR spectroscopy, DFT calculations, and Stern-Volmer plots. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.