Molekularer Rubin unter Druck

Abstract

Die intensiv lumineszierenden Chrom(III)-Komplexe [Cr(ddpd) 2 ] 3+ und [Cr(H 2 tpda) 2 ] 3+ zeigen eine überraschende druckinduzierte Rotverschiebung ihrer scharfen Spin-Flip-Emissionsbanden von bis zu À15 cm À1 kbar À1 (ddpd = N,N'-Dimethyl-N,N'-dipyridin-2-yl-pyridin-2,6-diamin; H 2 tpda = 2,6-Bis (2-pyridylamino)pyridin). Diese Verschiebung ist 20-mal stärker als die des etablierten Druckstandards Rubin Al 2 O 3 :Cr 3+ .D ie sehr hohe Quantenausbeute von [Cr-(ddpd) 2 ] 3+ erlaubt zudem sogar optische Druckmessungen in Wasser und Methanol. Diese einzigartigen Merkmale der molekularen Rubine [Cr(ddpd) 2 ] 3+ und [Cr(H 2 tpda) 2 ] 3+ ermçglichen hoch-empfindliche optische Druckmessungen und eine bislang beispiellose Druckmessung mithilfe eines einzigen molekularen Luminophor-Typs.

Towards Luminescent Vanadium(II) Complexes with Slow Magnetic Relaxation and Quantum Coherence

“… [8] A thoroughly studied ion with S = 3 / 2 is chromium(III). Chromium(III) complexes (quartet ground state, S = 3 / 2 ) with suitable ligand fields have been developed into highly versatile materials for photonic and photocatalytic applications, including sensing,[ 9 , 10 , 11 ] upconversion,[ 12 , 13 ] circularly polarized luminescence[ 14 , 15 ] and photo(redox) catalysis. [ 16 , 17 , 18 , 19 ] The magnetic ground state S = 3 / 2 of the highly luminescent molecular ruby [Cr(ddpd) 2 ] 3+ with the spin‐flip [20] emission band peaking at 778 nm [21] shows a long coherence time of 8.4(1) μs (ddpd= N , N ’‐dimethyl‐ N , N ’‐dipyridine‐2‐yl‐pyridine‐2,6‐diamine).…”

Quantum Chemical Study of the Pressure‐dependent Phosphorescence of [Cr(ddpd)2]3+in the Solid State

“…From high‐level CASSCF‐NEVPT2 calculations the lowest emissive state (energy E 2 ) derives from a spin‐paired spin‐flip state of 2 T 1 origin, while the higher emissive state (energy E 1 ) derives from a true spin‐flip state of 2 E origin (Figure 1). [7b,8c] In contrast, the lowest emissive state is reported as a 2 E state for the classical chromium(III) complexes such as [Cr(ox) 3 ] 3− , [Cr(NH 3 ) 6 ] 3+ , [Cr(urea) 6 ] 3+ and [CrF 6 ] 3− [13–16] …”

“…With the development of the highly emissive molecular polypyridine chromium(III) complex [Cr(ddpd) 2 ] 3+[17] and its congeners (molecular rubies), [2b,18–20] very large pressure‐induced shifts Δ$${\tilde{v}}$$ 2 /Δ p of −13.0 to −14.1 cm −1 kbar −1 have been achieved in the solid state (Table 1; energy E 2 ) [7b] . Spin‐flip emitters with other metal ions or d electron configurations [21] can show different behavior, which might also depend on the ground state splitting [22] .…”

“… Computationally derived state diagram at the ground state geometry of [Cr(ddpd) 2 ] 3+ with dominating electron configurations in the microstates and calculated spin‐densities at an isosurface value of 0.05 a.u. of states relevant to this study [7b,8c] …”

“…The exceptionally large quantum yields and solubility of the molecular rubies in water or methanol allowed the detection of pressure‐induced shifts for both emission bands even in solution (Table 1). [7b] When changing the counter ions or the environment (crystal/solution), the more pronounced shift of the 2 T 1 → 4 A 2 ( E 2 ) emission band of [Cr(ddpd) 2 ] 3+ varies merely between −13.0 and −14.8 cm −1 kbar −1 , while the shift of the higher‐energy band 2 E→ 4 A 2 ( E 1 ) is more affected with a variation from −4.7 to −9.8 cm −1 kbar −1 [7b] . Consequently, the energy gap between the two lowest emissive doublet states of 2 E and 2 T 1 character increases with increasing pressure, but to a different extent in varying environments.…”