D→f energy transfer in heteronuclear Ir(III)/Ln(III) near-infrared luminescent complexes

A series of d/f dinuclear complexes Ir•Ln [where Ln = Eu(III), Gd(III), Yb(III) and Nd(III)] are reported. The core structure consists of a rigid skeleton containing two different types of receptor site in a single molecular motif designed to combine a transition metal ion [Ir(III)] and a lanthanide ion [Ln(III)] in different binding sites at either end of fully conjugated bridge to facilitate d → f energy-transfer following photoexcitation of the Ir(III)-based antenna unit. Steady state and time-resolved photophysical experiments on these compounds revealed that the energy-transfer is feasible only in case of Ir•Yb and Ir•Nd systems, affording sensitized emission from the Yb(III) or Nd(III) centres. Such EnT is not possible in the Ir•Eu dyad as the excited state energy of the Ir(III) unit is insufficient to sensitise the excited state of the Eu(III) centre.