Strongly Red-Emissive Molecular Ruby [Cr(bpmp)2]3+ Surpasses [Ru(bpy)3]2+
Open Access
- 23 July 2021
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 143 (30), 11843-11855
- https://doi.org/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.Funding Information
- Deutsche Forschungsgemeinschaft (GE 961/10-1, HE 2778/15-1, RE 1203/23-1, SE 1448/8-1)
This publication has 109 references indexed in Scilit:
- Theoretical study on ultrafast intersystem crossing of chromium(III) acetylacetonateChemical Physics Letters, 2012
- Near‐Infrared→Visible Light Upconversion in a Molecular Trinuclear d–f–d ComplexAngewandte Chemie, 2011
- Transition metals compounds: Outstanding challenges for multiconfigurational methodsInternational Journal of Quantum Chemistry, 2011
- Vibrational coherence in the excited state dynamics of Cr(acac)3: probing the reaction coordinate for ultrafast intersystem crossingChemical Science, 2010
- Reevaluation of absolute luminescence quantum yields of standard solutions using a spectrometer with an integrating sphere and a back-thinned CCD detectorPhysical Chemistry Chemical Physics, 2009
- Recent progress in ligand field theoryPublished by Springer Science and Business Media LLC ,2008
- Absorption and Emission Spectroscopy of a Lasing Material: RubyJournal of Chemical Education, 2007
- Structural and photophysical properties of LnIII complexes with 2,2′-bipyridine-6,6′-dicarboxylic acid: surprising formation of a H-bonded network of bimetallic entities†J. Chem. Soc., Dalton Trans., 2000
- Chemical Redox Agents for Organometallic ChemistryChemical Reviews, 1996
- Electron transfer quenching of excited states of metal complexesJournal of the American Chemical Society, 1976