Direct Determination of the Rate of Intersystem Crossing in a Near-IR Luminescent Cr(III) Triazolyl Complex

Robert Jones, Alexander Auty, Guanzhi Wu, Petter Persson, Martin Appleby, Dimitri Chekulaev, Craig Rice, Julia A. Weinstein, Paul Elliott, Paul Scattergood

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


A detailed understanding of the dynamics of photoinduced processes occurring in the electronic excited state is essential in informing the rational design of photoactive transition-metal complexes. Here, the rate of intersystem crossing in a Cr(III)-centered spin-flip emitter is directly determined through the use of ultrafast broadband fluorescence upconversion spectroscopy (FLUPS). In this contribution, we combine 1,2,3-triazole-based ligands with a Cr(III) center and report the solution-stable complex [Cr(btmp) 2] 3+ (btmp = 2,6- bis(4-phenyl-1,2,3-triazol-1-yl-methyl)pyridine) ( 1 3+ ), which displays near-infrared (NIR) luminescence at 760 nm (τ = 13.7 μs, ϕ = 0.1%) in fluid solution. The excited-state properties of 1 3+ are probed in detail through a combination of ultrafast transient absorption (TA) and femtosecond-to-picosecond FLUPS. Although TA spectroscopy allows us to observe the evolution of phosphorescent excited states within the doublet manifold, more significantly and for the first time for a complex of Cr(III), we utilize FLUPS to capture the short-lived fluorescence from initially populated quartet excited states immediately prior to the intersystem crossing process. The decay of fluorescence from the low-lying 4MC state therefore allows us to assign a value of (823 fs) -1 to the rate of intersystem crossing. Importantly, the sensitivity of FLUPS to only luminescent states allows us to disentangle the rate of intersystem crossing from other closely associated excited-state events, something which has not been possible in the spectroscopic studies previously reported for luminescent Cr(III) systems.

Original languageEnglish
Pages (from-to)12081-12092
Number of pages12
JournalJournal of the American Chemical Society
Issue number22
Early online date24 May 2023
Publication statusPublished - 7 Jun 2023


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