Synthesis, One- and Two-Photon Photophysical and Excited-State Properties, and Sensing Application of a New Phosphorescent Dinuclear Cationic Iridium(III) Complex

A new phosphorescent dinuclear cationic iridium(III) complex (Ir1) with a donor-acceptor-pi-bridge-acceptor-donor (D-A-pi-A-D)-conjugated oligomer (L1) as a N<^>N ligand and a triarylboron compound as a C<^>N ligand has been synthesized. The photophysical and excited-state properties of Ir1 and L1 were investigated by UV/Vis absorption spectroscopy, photoluminescence spectroscopy, and molecular-orbital calculations, and they were compared with those of the mononuclear iridium(III) complex [Ir(Bpq)(2)(bpy)]+PF6- (Ir0). Compared with Ir0, complex Ir1 shows a more-intense optical-absorption capability, especially in the visible-light region. For example, complex Ir1 shows an intense absorption band that is centered at lambda=448 nm with a molar extinction coefficient (epsilon) of about 10(4), which is rarely observed for iridium(III) complexes. Complex Ir1 displays highly efficient orange-red phosphorescent emission with an emission wavelength of 606 nm and a quantum efficiency of 0.13 at room temperature. We also investigated the two-photon-absorption properties of complexes Ir0, Ir1, and L1. The free ligand (L1) has a relatively small two-photon absorption cross-section (delta(max)=195 GM), but, when complexed with iridium(III) to afford dinuclear complex Ir1, it exhibits a higher two-photon-absorption cross-section than ligand L1 in the near-infrared region and an intense two-photon-excited phosphorescent emission. The maximum two-photon-absorption cross-section of Ir1 is 481 GM, which is also significantly larger than that of Ir0. In addition, because the strong B-F interaction between the dimesitylboryl groups and F- ions interrupts the extended pi-conjugation, complex Ir1 can be used as an excellent one-and two-photon-excited ON-OFF phosphorescent probe for F- ions.