Electronic Nature of New Ir(III) Complexes: Linear Spectroscopic and Nonlinear Optical Properties

Comprehensive investigations of the linear and nonlinear optical properties of new Ir(III) complexes [Ir(pbt)2(dbm)] (1), [Ir(pbt)2(dmac)] (2), and [Ir(pbt)2(minc)] (3) (pbt = 2-phenylbenzothiazole; dbm = dibenzoyl methane; dmac = (1E,4Z,6E)-1,7-bis(4-(dimethylamino)phenyl)-5-hydroxyhepta-1,4,6-trien-3-one; minc = (1E,4Z,6E)-5-hydroxy-1,7-bis(1-methyl-1H-indol-3-yl)hepta-1,4,6-trien-3-one) are reported, including photostability, two-photon absorption, and femtosecond transient absorption spectroscopy. The steady-state and time-resolved spectral properties of 1–3revealed the electronic nature of the absorption bands, and photoluminescence emission of 2and 3shows both fluorescence and phosphorescence processes occurring simultaneously in liquid solution at room temperature. This unusual behavior of 2and 3can be explained by a dual-minimum potential surface of the excited electronic state resulting in two independent fluorescence and phosphorescence emission channels. The degenerate 2PA spectra of 1–3were obtained by open aperture Z-scans with a femtosecond laser, and maxima values of 2PA cross sections up to ∼350 GM were observed. Ultrafast relaxation processes of 1–3were investigated by femtosecond transient absorption, and the characteristic times for triplet formation were determined to be <500 fs for 1and ∼2 ps for 2and 3in a nonpolar medium.