Molecular ruby: exploring the excited state landscape

Abstract

The discovery of the highly NIR-luminescent Molecular Ruby [Cr(ddpd)2]3+ 13+ (ddpd = N,N’-dimethyl-N,N’-dipyridine-2-ylpyridine-2,6-diamine) has been a milestone in the development of earth-abundant luminophors and has led to important new impulses...

Shedding Light on the Oxidizing Properties of Spin-Flip Excited States in a CrIII Polypyridine Complex and Their Use in Photoredox Catalysis

“…The 2 E state is typically energetically below the 2 T 1 state for most Cr III complexes with pseudo-octahedral geometry, 28,30,49 though there seem to be exceptions. 27,38,39,50 In cyclic voltammetry, the first reduction of [Cr(dqp) 2 ] 3+ is observed at −0.4 V vs SCE (Figure S1), in line with the literature. 28 Consequently, a potential of −0.5 V vs SCE was applied for reductive UV−vis (Figure 2b, green trace) and NIR spectro-electrochemistry (Figure S3).…”

“…At 77 K, only the emission at 747 nm remains observable (Figure a, red dotted trace). The 2 E state is typically energetically below the 2 T 1 state for most Cr III complexes with pseudo-octahedral geometry, ,, though there seem to be exceptions. ,,, …”

“…The 2 E state is typically energetically below the 2 T 1 state for most Cr III complexes with pseudo-octahedral geometry, 28 , 30 , 49 though there seem to be exceptions. 27 , 38 , 39 , 50 …”

Complex-as-Ligand Strategy as a Tool for the Design of a Binuclear Nonsymmetrical Chromium(III) Assembly: Near-Infrared Double Emission and Intramolecular Energy Transfer

“…The excitation spectra show marked shoulders at 455 nm ( ṽ = 23474 cm –1 ) and 546 nm ( ṽ = 18587 cm –1 ), which can be assigned to the ligand-field transition Cr III ( 4 T 2 ← 4 A 2 ) characterizing each [Cr­(phen) 3 ] 3+ and [Cr­(tpy)­(bzpy)] 3+ moiety . The considerable relative intensities of the latter bands in the excitation spectra (Figure ), compared with those in the absorption spectrum (Figure S5), suggest some efficient Cr­( 4 T 2 → 2 T 2 ) intersystem crossing for eventually populating the emissive 2 T 1 and 2 E levels. , …”

“…Chromium polypyridyl complexes have received increasing attention during the past decade because of their robustness and their long-lived near-infrared (NIR) emission. − Important efforts were provided to tune the spin-flip emission energy − and to extend the excited-state lifetime to the millisecond range at room temperature. − Recently, the chirality of Cr III complexes has been harnessed to implement circularly polarized luminescence (CPL), which results in impressive dissymmetry factors approaching those of rare-earth centers. ,,,− Even if chromium­(III) polypyridyl chromophores display appealing features as mononuclear complexes, their incorporation into polymetallic architectures is required for the exploitation of novel emission properties such as directional NIR to NIR downshifting , or CPL emission boosted by indirect sensitization . However, the synthetic pathways able to combine several chromium­(III) polypyridyl units within a single (supra)­molecule are scarce, and we are only aware of (i) the self-assembly of CrLnCr triple helices displaying molecular-based upconversion − and (ii) the design of centrosymmetrical binuclear chromium­(III) polypyridyl complexes separated by back-to-back bis­(terpyridine) bridging ligands showing weak-to-negligible intermetallic communication .…”