Strongly Red-Emissive Molecular Ruby [Cr(bpmp)2]3+Surpasses [Ru(bpy)3]2+

Reichenauer F, Wang C, Forster C, Boden P, Ugur N, Baez-Cruz R, Kalmbach J, Carrella LM, Rentschler E, Ramanan C, Niedner-Schatteburg G, Gerhards M, Seitz M, Resch-Genger U, Heinze K (2021)

Publication Type: Journal article

Publication year: 2021

Journal

Journal of the American Chemical Society American Chemical Society

Book Volume: 143

Pages Range: 11843-11855

Journal Issue: 30

DOI: 10.1021/jacs.1c05971

Abstract

Gaining chemical control over the thermodynamics and kinetics of photoexcited states is paramount to an efficient and sustainable utilization of photoactive transition metal complexes in a plethora of technologies. In contrast to energies of charge transfer states described by spatially separated orbitals, the energies of spin-flip states cannot straightforwardly be predicted as Pauli repulsion and the nephelauxetic effect play key roles. Guided by multireference quantum chemical calculations, we report a novel highly luminescent spin-flip emitter with a quantum chemically predicted blue-shifted luminescence. The spin-flip emission band of the chromium complex [Cr(bpmp)2]3+ (bpmp = 2,6-bis(2-pyridylmethyl)pyridine) shifted to higher energy from ca. 780 nm observed for known highly emissive chromium(III) complexes to 709 nm. The photoluminescence quantum yields climb to 20%, and very long excited state lifetimes in the millisecond range are achieved at room temperature in acidic D2O solution. Partial ligand deuteration increases the quantum yield to 25%. The high excited state energy of [Cr(bpmp)2]3+ and its facile reduction to [Cr(bpmp)2]2+ result in a high excited state redox potential. The ligand's methylene bridge acts as a Brønsted acid quenching the luminescence at high pH. Combined with a pH-insensitive chromium(III) emitter, ratiometric optical pH sensing is achieved with single wavelength excitation. The photophysical and ground state properties (quantum yield, lifetime, redox potential, and acid/base) of this spin-flip complex incorporating an earth-abundant metal surpass those of the classical precious metal [Ru(α-diimine)3]2+ charge transfer complexes, which are commonly employed in optical sensing and photo(redox) catalysis, underlining the bright future of these molecular ruby analogues.

Involved external institutions

Johannes Gutenberg-Universität Mainz (JGU) DE Germany (DE) Bundesanstalt für Materialforschung und -prüfung (BAM) DE Germany (DE) Technische Universität Kaiserslautern DE Germany (DE) Max-Planck-Institut für Polymerforschung (MPI-P) / Max Planck Institute for Polymer Research DE Germany (DE) Eberhard Karls Universität Tübingen DE Germany (DE)

How to cite

APA:

Reichenauer, F., Wang, C., Forster, C., Boden, P., Ugur, N., Baez-Cruz, R.,... Heinze, K. (2021). Strongly Red-Emissive Molecular Ruby [Cr(bpmp)2]3+Surpasses [Ru(bpy)3]2+. Journal of the American Chemical Society, 143(30), 11843-11855. https://doi.org/10.1021/jacs.1c05971

MLA:

Reichenauer, Florian, et al. "Strongly Red-Emissive Molecular Ruby [Cr(bpmp)2]3+Surpasses [Ru(bpy)3]2+." Journal of the American Chemical Society 143.30 (2021): 11843-11855.

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