Linear and nonlinear optical properties of cationic bipyridyl iridium(III) complexes: tunable and photoswitchable?

A series of cationic Ir(III) substituted bipyridyl (N∧N (N∧N-bpy) complexes incorporating electron-donor and -acceptor substituents, [Ir(C∧N-ppy-R′)2(N∧N-bpy-CH═CH-C6H4-R)][X] (X– = PF6– or C12H25SO3–), 2 (a, R = NEt2 and R′ = Me; b, R = O-Oct and R′ = Me; c, R = NO2 and R′ = C6H13; C∧N-ppy = cyclometalated 2-phenylpyridine, [Ir(C∧N-ppy-Me)2(N∧N-bpy-CH═CH-thienyl-Me)][PF6], 2d, and the dithienylethene (DTE)-containing complex 2e have been synthesized and characterized, and their absorption, luminescence, and quadratic nonlinear optical (NLO) properties are reported. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations on the complexes facilitate a detailed assignment of the excited states involved in the absorption and emission processes. All five complexes are luminescent in a rigid glass at 77 K, displaying vibronically structured spectra with long lifetimes (14–90 μs), attributed to triplet states localized on the styryl-appended bipyridines. The second-order NLO properties of 2...