Iridium(III)-Doped Core-Shell Silica Nanoparticles: Near-IR Electrogenerated Chemiluminescence in Water

The electrogenerated chemiluminescence (ECL) properties of two neutral cyclometalated Ir(III) complexes, Ir(iqbt)2dpm (1) and its parent complex fac-Ir(iqbt)3 (2) [iqbt=1-(benzo[b]thiophen-2-yl)-isoquinolinate], have been investigated in acetonitrile solution. Complexes 1 and 2 display near-infrared (near-IR) ECL emission in acetonitrile with maxima at 712 and 706 nm, respectively. Species 1 and 2 showed a strong increase in ECL intensity upon employing benzoyl peroxide (BPO) as a co-reactant with respect to the annihilation. The remarkable continuous ECL emission in near-IR region makes these complexes promising candidates for development of near-IR-emitting Ir-based labels in diagnostics. Furthermore, encapsulation of complex 1 within silica-PEG nanoparticles was successfully obtained: the resulting 1@NPs are easily solubilized in aqueous media where remarkable ECL emission was observed even in aerated conditions.