Optimizing Millisecond Time Scale Near-Infrared Emission in Polynuclear Chrome(III)–Lanthanide(III) Complexes

Abstract

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.

Enhancement of Optical Faraday Effect of Nonanuclear Tb(III) Complexes

“…16,17 Piguet and co-workers reported the enhancement of the luminescence of polynuclear complexes by effective energy transfer from Cr(III) to lanthanide(III) ions. 18 We also recently demonstrated temperature-sensitive luminophores composed of Eu-(III) and Tb(III) complexes. 19 Specific metal-to-metal interactions in polynuclear lanthanide complexes induce active magnetic and photophysical behavior.…”

Broadband Cr^3+-sensitized upconversion luminescence in La_3Ga_5GeO_14: Cr^3+,Yb^3+,Er^3+

“…It is reported that La 3 Ga 5 GeO 14 :Cr 3+ exhibited excellent near infrared emission at around 980 nm with broadband absorption at 370~520 nm and 560~800 nm [32,33]. It can be deduced that Cr 3+ could efficiently transfer its absorbed energy to Yb 3+ in La 3 Ga 5 GeO 14 through resonant energy transfer based on the matching of emission energy level of Cr 3+ and absorption energy level of Yb 3+ at around 980 nm, which are proved by many previous work [10,21,22,24]. The absence of absorption at 520~560 nm makes Cr 3+ probable to sensitize Yb 3+ -Er 3+ with room-temperature UC luminescence of Er 3+ in this wavelength range, which is further convinced by the fact that La 3+ site could accommodate Yb 3+ /Er 3+ and Ga 3+ site could accommodate Cr 3+ with less distortion defects as emission killer.…”

“…Herein, to get high energy transfer efficiency, short distance and the matching of energy levels between sensitizer(dye molecules) and acceptor(Yb 3+ -Er 3+ ) are required for resonant energy transfer pathway [19,20]. It is known that transition metal(TM) ions have the broadband absorption feature, which is commonly utilized to sensitize Stokes luminescence of lanthanide ions [21,22]. Analogously, they could also be used as a broadband sensitizer for UC luminescence [7,10], for instance, the Cr 5+ -Er 3+ [23], V 3+ -Er 3+ [24,25] and V 3+ -Pr 3+ [26] systems.…”

Supramolecular Chirality in Dynamic Coordination Chemistry

“…Chirality in octahedral systems is interesting because many metal cations favor octahedral geometry and can provide more complex, dynamic, and functional systems including triple helicates [55,56], circular helicates [57,58], tetrahedral clusters [59], and heteronuclear helicates consisting of lanthanide and transition metal cations [60][61][62]. Chirality induction in octahedral metal complexes has been widely investigated using chiral ligands, starting with Werner's pioneering works [29,30], in which most metal centers were kinetically inert; their complexations often required long periods of time for completion, and purification procedures were required for obtaining diastereo-and enantiopure complexes.…”