Optimizing millisecond time scale near-infrared emission in polynuclear chrome(III)-lanthanide(III) complexes.
This work illustrates a simple approach for optimizing long-lived near-infrared lanthanide-centered luminescence using trivalent chromium chromophores as sensitizers. Reactions of the segmental ligand L2 with stoichiometric amounts of M(CF(3)SO(3))(2) (M = Cr, Zn) and Ln(CF(3)SO(3))(3) (Ln = Nd, Er, Yb) under aerobic conditions quantitatively yield the D(3)-symmetrical trinuclear [MLnM(L2)(3)](CF(3)SO(3))(n) complexes (M = Zn, n = 7; M = Cr, n = 9), in which the central lanthanide activator is sandwiched between the two transition metal cations. Visible or NIR irradiation of the peripheral Cr(III) chromophores in [CrLnCr(L2)(3)](9+) induces rate-limiting intramolecular intermetallic Cr→Ln energy transfer processes (Ln = Nd, Er, Yb), which eventually produces lanthanide-centered near-infrared (NIR) or IR emission with apparent lifetimes within the millisecond range. As compared to the parent dinuclear complexes [CrLn(L1)(3)](6+), the connection of a second strong-field [CrN(6)] sensitizer in [CrLnCr(L2)(3)](9+) significantly enhances the emission intensity without perturbing the kinetic regime. This work opens novel exciting photophysical perspectives via the buildup of non-negligible population densities for the long-lived doubly excited state [Cr*LnCr*(L2)(3)](9+) under reasonable pumping powers.
Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, Geneva, Switzerland.
Lilit
L
Aboshyan-Sorgho
Homayoun
H
Nozary
Annina
A
Aebischer
Jean-Claude G
JC
Bünzli
Pierre-Yves
PY
Morgantini
Kevin R
KR
Kittilstved
Andreas
A
Hauser
Svetlana V
SV
Eliseeva
Stéphane
S
Petoud
Claude
C
Piguet
D002857:Chromium / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D004735:Energy Transfer; D028581:Lanthanoid Series Elements / Q000138:chemical synthesis / Q000737:chemistry*; D008027:Light; D049449:Luminescence; D049408:Luminescent Agents / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D019265:Spectroscopy, Near-Infrared
D056831:Coordination Complexes; D028581:Lanthanoid Series Elements; D049408:Luminescent Agents; D002857:Chromium