Scientific article
OA Policy
English

Modulating the spin–flip rates and emission energies through ligand design in chromium(iii) molecular rubies

Published inChemical science, vol. 16, no. 12, 5205-5213
First online date2025
Abstract

Three homoleptic spin-flip (SF) emitters, namely [Cr(Mebipzp)2 ]3+ (1), [Cr(IMebipzp)2 ]3+ (2) and [Cr(bip*)2 ]3+ (3), have been successfully synthesized and characterized. The weak distortion compared to a perfect octahedron imparts favourable structural properties to the three complexes, which display spin-flip (SF) luminescence at approximately 740 nm with quantum yields in the range of 9-11% for 1 and 2 in deaerated acetonitrile solutions at 25 °C. Time-resolved luminescence and transient UV-vis absorption experiments unveiled lifetimes for the lowest-lying 2 MC (metal-centered) of 1.5 ms for 1 and 350 μs for 2. The incorporation of iodine atoms onto the ligand scaffold in 2 accelerates the 2 MC → 4 A2 relaxation process through simultaneous enhancements in the radiative and non-radiative rate constants. In agreement, the experimentally calculated absorption oscillator strength for the 2 MC ← 4 A2 transition amounts to 9.8 × 10-7 and 2.5 × 10-6 for 1 and 2, respectively. The 2.5 factor enhancement observed in the iodine derivative indicates a higher spin-flip transition probability, translating into higher values of radiative rate constant (k rad ). Interestingly, in compound 3, the substitution of the distal methyl-pyrazole with indazole rings causes an important bathochromic shift of the SF emission energy to 12 000 cm-1 (830 nm). Likely, the extended π-system and the more covalent bond character induced by the indazole decrease the interelectronic repulsion further stabilizing the SF excited states. The recorded excited state lifetime of 111 μs in 3 remains among the longest for a molecular ruby emitting beyond 800 nm. These discoveries signify an underexplored avenue for modifying deactivation pathways and emission energy while retaining high quantum yields and long-lived excited states in molecular rubies.

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YE, Yating et al. Modulating the spin–flip rates and emission energies through ligand design in chromium(iii) molecular rubies. In: Chemical science, 2025, vol. 16, n° 12, p. 5205–5213. doi: 10.1039/d4sc08021a
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Additional URL for this publicationhttps://xlink.rsc.org/?DOI=D4SC08021A
Journal ISSN2041-6520
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