Synthesis and properties of a dendritic FRET donor-acceptor system with cationic iridium(III) complex core and...

In order to enhance the photoluminescence of cyclometalated iridium(III) complexes, which are potentially useful for biolabeling and bioimaging, a series of benzyl ether branched dendritic moieties with carbazolyl termini were introduced to the cyclometalating C^N ligands of the heteroleptic Ir(III) complexes. The complexes also contain a bidentate bipyridine ligand with a carboxyl group for further bioconjugation or functionalization. The dendritic benzyl ether moieties with carbazolyl peripheral groups have demonstrated a dual function as both a Förster resonance energy transfer (FRET) donor and an oxygen shield to the Ir(III) complex core. The peripheral carbazolyl groups absorb UV light more intensively and transfer energy efficiently to the Ir(III) complex core via the FRET effect, and thus the photoluminescence of the Ir(III) complex at around 560 nm is significantly enhanced. Furthermore, the benzyl ether dendrimers containing carbazolyl termini can shield the Ir(III) complex core to weaken the oxygen quenching effect, which leads to a further enhancement of the PL of the Ir(III) complex.