Photophysics and excited-state absorption of bis-cyclometalated iridium complexes with isocyanide ancillary ligands

Cyclometalated iridium complexes have long been prominent in electroluminescent applications, and several recent studies have shown that this family of compounds offers several potential advantages for designing materials with reversesaturable absorption (RSA) and other nonlinear optical properties. In this talk we present a comprehensive study of the excited-state properties of three bis-cyclometalated iridium complexes of the general formula [Ir(C^N)2(CNdmp)2]+, where C^N is a variable cyclometalating ligand and CNdmp is 2,6-dimethylisocyanide. The ground-state absorption and photoluminescence (PL) properties are described, with the identity of the cyclometalating ligand having a large effect on the observed PL wavelength. When the cyclometalating ligand is 2-phenylbenzothiazole (pbt), intense yellow PL is observed, whereas the PL with nitro-substituted 9-pyridylphenanthrene or 2-phenylpyridine C^N ligands is red-shifted and much weaker. Transient absorption (TA) spectroscopy was used to evaluate the excited-state absorption of the compounds. TA spectra indicate broad and intense excited-state absorption for all three compounds, with the wavelength profile strongly determined by the cyclometalating ligand. TA lifetimes are consistent with PL lifetimes and strongly oxygendependent, indicating that excited-state absorption that arises from a triplet state. To evaluate the effects of the CNdmp isocyanide ancillary ligands, we include comparisons to charge-neutral Ir(C^N)2(acac) (acac = acetylacetonate) complexes with the same C^N ligands. The isocyanide compounds have substantially blue-shifted ground-state absorption, excitedstate absorption, and PL, and in most cases longer lifetimes compared to the acac analogues.