Two new heteroleptic cationic Ir(III) complexes bearing benzothiazole and pyridine motif on the fluorene (C^N) and fluorene motif on bipyridine (N^N) ligands were synthesized and characterized. Both complexes exhibit 1π-π* transitions below 450 nm, with broad but weak metal-to ligand and ligand-to-ligand charge transfer (MLCT/LLCT) absorption bands between 450 nm. Complexes Ir1 and Ir2 possesses long-lived emission (τem = 0.271 μs for Ir1, τem = 5.811 μs for Ir2) and triplet excited states (τTA = 0.315 μs for Ir1, τTA = 4.341 μs for Ir2). Both Ir(III) complexes exhibit aggregation-induced emission (AIE) behavior in acetonitrile-water mixture. As the contents of water were added up to 90%, the fluorescence emission intensity of complexes Ir1 and Ir2 increased nearly 3 times and 2.8 times, respectively. Moreover, the optical power limiting (OPL) performance in the aggregated state was also investigated, the strength of reverse saturable absorption (RSA) at 532 nm followed the trend: Ir2 &gt; Ir1 . Replacing pyridine component with benzothiazole increased the RSA of the Ir(III) complexes due to its increased degree of π-conjugation. Complexes Ir1 and Ir2 are strong reverse saturable absorbers at 532 nm against laser pulses, which could be potentially used as OPL materials.

Fluorene-decorated Ir(III) complexes: tunable photophysical properties, reverse saturable absorption in solution and aggregated state

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