Luminescence and time-resolved infrared study of dyads containing (Diimine)Ru(4,4′-diethylamido-2,2′ -bipyridine)2 and (Diimine)Ru(CN)4 moieties: Solvent-induced reversal of the direction of photoinduced energy-transfer

Timothy L. Easun, Wassim Z. Alsindi, Nina Deppermann, Michael Towrie, Kate L. Ronayne, Xue Zhong Sun, Michael D. Ward, Michael W. George

Research output: Journal PublicationArticlepeer-review

33 Citations (Scopus)

Abstract

The exploitation of the dramatic negative solvatochromism of the [Ru(bipy)(CN)4] moiety (bipy = 2,2′-bipyridine) allows a change in solvent to reverse the direction of photoinduced energy transfer (PEnT) in two related dinuclear complexes. Both dyads consist of a [Ru(bpyam) 2Ln]2+ (Ru-bpyam) unit (bpyam = 4,4′-diethylamido-2,2′-bipyridine; Ln = bis-bipyridyl-based bridging ligand) and a [Ru(Ln)(CN)4] (Ru-CN) unit. Both termini have IR-active spectroscopic handles (amide carbonyl or cyanide, respectively) allowing the excited-state dynamics to be studied by time-resolved IR (TRIR) spectroscopy. One dyad (1) contains a relatively rigid exoditopic macrocyclic bis-bipyridyl bridging ligand (L1) and the other (2) contains a more flexible bis-bipyridyl bridging ligand with only one covalent linkage between the two bipyridyl binding sites (L2). The conformational effects on PEnT rates in these dyads are probed using a combination of luminescence and TRIR studies. In both 1 and 2 in D2O it is demonstrated that Ru-CN -Ru-bpyam PEnT occurs (PEnT time scales were in the range 10 ps-3 ns) because the 3MLCT energy of the Ru-CN terminus is higher than that of the Ru-bpyam terminus. Changing the solvent from D 2O to CH3CN results in lowering the 3MLCT energy of the Ru-CN unit below that of the Ru-bpyam unit such that in both dyads a reversal in the direction of PEnT to Ru-bpyam -Ru-CN (time scales of 10 ps-2 ns) occurs. Complex kinetic behavior results from the presence of a dark 3MLCT excited state formulated as {(bpyam)2Ru 3+(Ln•-)} and by the presence of multiple conformers in solution which have different Ru ⋯ Ru separations giving rise to different energy transfer rates.

Original languageEnglish
Pages (from-to)8759-8770
Number of pages12
JournalInorganic Chemistry
Volume48
Issue number18
DOIs
Publication statusPublished - 21 Sep 2009
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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