Synthesis, Characterization, and Properties of Doubly Alkynyl Bridging Dinuclear Cyclometalated Iridium(III) Complexes

Abstract

Bis­(cyclometalated) diiridium complexes [Ir­(ppy)2(μ–κC α:η2-CCR)]2 (R = Tol 1, C6H4OMe-4 2, 1-Np 3, SiMe3 4, t Bu 5), stabilized by a double alkynyl bridging system, have been synthesized by alkynylation of [Ir­(ppy)2(μ-Cl)]2 with excess of the appropriate LiCCR (1:6 or 1:10 molar ratio). Complexes 1–3 were alternatively generated by treatment of [Ir­(ppy)2(MeCN)2]­(OTf) with 2.5 equiv of LiCCR. However, the related reaction with LiCC t Bu evolves with the formation of mixtures from which the unexpected dinuclear complex [Ir­(ppy)2(μ-CH2CN)]2 6 was crystallized, as confirmed by X-ray diffraction studies. Complexes 1–5 have been characterized by NMR, IR, absorption and emission spectroscopies, cyclic voltammetry, and mass spectrometric methods. Characterization indicates that 1–3 and 5 are obtained as a unique diastereoisomer (ΛΛ/ΔΔ), whereas 4 gives the two diastereoisomers (ΔΛ and ΛΛ/ΔΔ). Single crystals of [Ir­(ppy)2(μ-CCTol)]2 1 contains the inversion related ΛΛ/ΔΔ isomers, and crystals of 4 (chosen from a mixture of two different types of crystals) consist of the meso-ΔΛ isomer. Electrochemical studies showed the presence in 1–3 and 5 of two consecutive one-electron-oxidation IrIII/IrIV processes, whereas 4 displayed only one irreversible oxidation peak. In degassed fluid solutions, complexes 1–5 are emissive in the 505–515 nm region with quantum yields higher (ϕ = 0.007–0.024) than that of the dichloro bridged precursor (0.0037). The influence of the alkynyl substituent in the emissive state at room and at low temperatures has been investigated. For the naphthylacetylide derivative 3, a clear switch from a mixed charge transfer 3MLCT/3L′LCT excited state at 298 K (515 nm) to a characteristic long-lived low lying naphthalene emission at low temperature (77 K) is observed. DFT and TD-DFT calculations were performed on complexes 1 and 3 in the ground and triplet states to gain insight into the structural, electronic, and photophysical properties.

Synthesis, Diastereomer Separation, and Optoelectronic and Structural Properties of Dinuclear Cyclometalated Iridium(III) Complexes with Bridging Diarylhydrazide Ligands

“…[44][45][46] In diiridium complexes, which incorporate conjugated bridging ligands, theoretical calculations often predict that a degree of frontier orbital character is localized on the bridging unit. 23,26,29,32,35,[37][38][39][40]42 In these cases a highly flexible bridge is expected to promote nonradiative processes and weaken emission. Consequently, the majority of the reported diiridium complexes that possess high solution state PLQYs incorporate rigid bridging units (such as compounds 4 and 6).…”

Alkynyl bridged cyclometalated Ir2M2 clusters: impact of the heterometal in the photo- and electro-luminescence properties

“…S23 †), which is ascribed to a mixture of 3 MLCT/ 3 L′LCT (L = ppy; L′ = CuCR) according to the previous theoretical calculations. 5 Similarly, 2 emits in the green region at 298 K (480-515 nm, Fig. 2 and S24 †).…”

“…S26 †), due to the well-known self-quenching process. 5 In stark contrast to 2, the emission of 3 is placed in the orange region (620-600 nm, Fig. 2 and S25 †).…”

“…S22 †) with only slight blue shifts in the low energy region [395 nm (2), 392 nm (3), and 406 nm (1)]. Previous studies on [Ir 2 ( ppy) 4 (µ-CuCTol) 2 ] 5 and TD-DFT analyses now conducted on optimized structures of 2 and 3 were used to interpret these spectra (Table S10, Fig. S27 †).…”

Bright green PhOLEDs using cyclometalated diiridium(iii) complexes with bridging oxamidato ligands as phosphorescent dopants

“…14 However, the m-dichloro-bridged dimers are generally very poorly emissive 15,16 (although there are a few exceptions). 17,18 Most other diiridium systems also have low luminescence quantum yields [19][20][21][22][23][24] which has focussed the vast majority of research onto the more strongly emissive monoiridium complexes. [1][2][3] However, the bridging ligands within diiridium complexes provide unique potential for additional structural and electronic variations compared to monoiridium systems.…”