Tuning the decay time of lanthanide-based near infrared luminescence from micro- to milliseconds through d->f energy transfer in discrete heterobimetallic complexes

Inert and optically active pseudo-octahedral Cr III N6 and Ru II N6 chromophores have been incorporated by self-assembly into heterobimetallic triple-stranded helicates HHH- (CrLnL3) 6 + and HHH-(RuLnL3) 5 + .T he crystal structures of (CrLnL3)(CF3SO3)6 (Ln = Nd, Eu, Yb, Lu) and (RuLnL3)- (CF3SO3)5 (Ln = Eu, Lu) demonstrate that the helical structure can accommo- date metal ions of different sizes, with- out sizeable change in the intermetallic M···Ln distances. These systems are ideally suited for unravelling the mo- lecular factors affecting the intermetal- lic nd!4f communication. Visible irra- diation of the Cr III N6 and Ru II N6 chro- mophores in HHH-(MLnL3) 5/6 + (Ln = Nd, Yb, Er; M = Cr, Ru) eventually produces lanthanide-based near infra- red (NIR) emission, after directional energy migration within the complexes. Depending on the kinetic regime asso- ciated with each specific d-f pair, the NIR luminescence decay times can be tuned from micro- to milliseconds. The origin of this effect, together with its rational control for programming opti- cal functions in discrete heterobimetal- lic entities, are discussed.