Optimizing millisecond time scale near-infrared emission in polynuclear chrome(III)-lanthanide(III) complexes

J Am Chem Soc. 2012 Aug 1;134(30):12675-84. doi: 10.1021/ja304009b. Epub 2012 Jul 19.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chromium / chemistry*
  • Coordination Complexes / chemical synthesis
  • Coordination Complexes / chemistry*
  • Energy Transfer
  • Lanthanoid Series Elements / chemical synthesis
  • Lanthanoid Series Elements / chemistry*
  • Light
  • Luminescence
  • Luminescent Agents / chemical synthesis
  • Luminescent Agents / chemistry*
  • Models, Molecular
  • Spectroscopy, Near-Infrared

Substances

  • Coordination Complexes
  • Lanthanoid Series Elements
  • Luminescent Agents
  • Chromium