Issue 28, 2022

Water-soluble ruthenium complex-pyrene dyads with extended triplet lifetimes for efficient energy transfer applications

Abstract

Long triplet lifetimes of excited photosensitizers are essential for efficient energy transfer reactions in water, given that the concentrations of dissolved oxygen and suitable acceptors in aqueous media are typically much lower than in organic solvents. Herein, we report the design, synthesis and photochemical characterization of two structurally related water-soluble ruthenium complex-based dyads decorated with a covalently attached pyrene chromophore. The triplet energy of the latter is slightly below that of the metal complex enabling a so-called triplet reservoir and excited-state lifetime extensions of up to two orders of magnitude. The diimine co-ligands, which can be modified easily, have a major impact on both the ultrafast intramolecular energy transfer (iEnT) kinetics upon excitation with visible light and the lifetime of the resulting long-lived pyrene triplet. The phenanthroline-containing dyad shows fast triplet pyrene formation (25 ps) and an exceptionally long triplet lifetime beyond 50 microseconds in neat water. The iEnT process via the Dexter mechanism is slower by a factor of two when bipyridine co-ligands are employed, which is rationalized by a poor orbital overlap. Both dyads are very efficient sensitizers for the formation of singlet oxygen in air-saturated water as well as for the bimolecular generation of anthracene triplets that are key intermediates in upconversion mechanisms. This is demonstrated by the 5-hydroxymethylfurfural oxidation, which yields completely different main products depending on the pH value of the aqueous solution, as an initial application-related experiment and by time-resolved spectroscopy. Our findings are important in the greater contexts of photocatalysis and energy conversion in the “green” solvent water.

Graphical abstract: Water-soluble ruthenium complex-pyrene dyads with extended triplet lifetimes for efficient energy transfer applications

Supplementary files

Article information

Article type
Paper
Submitted
13 Mme 2022
Accepted
13 Jan 2022
First published
28 Jan 2022

Dalton Trans., 2022,51, 10799-10808

Water-soluble ruthenium complex-pyrene dyads with extended triplet lifetimes for efficient energy transfer applications

A. C. Sell, J. C. Wetzel, M. Schmitz, A. W. Maijenburg, G. Woltersdorf, R. Naumann and C. Kerzig, Dalton Trans., 2022, 51, 10799 DOI: 10.1039/D2DT01157C

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