Enhanced deep red to near-infrared (DR-NIR) phosphorescence in cyclometalated iridium(iii) complexes

Abstract

Bis-cyclometalated iridium complexes with highly conjugated cyclometalating ligands and electron-rich ancillary ligands have exceptional quantum yields for deep-red to near-infrared phosphorescence.

Enhanced Deep-Red Phosphorescence in Cyclometalated Iridium Complexes with Quinoline-Based Ancillary Ligands

“…Full CV traces are shown in Figure S1, with the recorded potentials summarized graphically in Figure 1 43 Consistent with this notion, for complexes with the same C^N ligand (pphen or piqCN), the observed E red values occur at very similar potentials and are likewise nearly identical to the values we previously recorded for other complexes with the same C^N ligands. 39 The first reduction occurs between −2.07 and −2.17 The DFT calculations reveal that the LUMO is almost entirely centered on one C^N ligand, and the LUMO+1 is nearly degenerate and localized on the second C^N ligand. These observations are consistent with CV results described above that show one or two closely spaced reduction waves, indicating minimally altered LUMO energies across the series with the same C^N ligand.…”

“…In most cases, these values are significantly shorter than those of the previously described Ir(C^N) 2 (L^X) complexes with C^N = btph partnered with quinoline-derived ancillary ligands 42 and slightly longer than those of analogues where pphen and piqCN are paired up with other classes of electron-rich ancillary ligands. 39 To better understand the excited states, the Franck−Condon singlet and triplet excited states of piqCN-8OQ were computed via time-dependent DFT. The calculations demonstrate that the lowest-energy singlet excited state consists of a clean LUMO ← HOMO one-electron transition at 595 nm.…”

“…This strategy has produced compounds with Φ PL values as high 0.8 in the red region 40 and 0.5 in the DR-NIR region when 1-phenylisoquinoline (piq) and substituted analogues are used as the cyclometalating (C^N) ligands. 39,41 In the course of these previous efforts, we found that the effectiveness of electron-rich ancillary ligands depends on the nature of the C^N ligands. In general, complexes with the electron-rich thiophenebased C^N ligands have photoluminescence properties that vary little as the ancillary ligand is changed, but when C^N ligands have simple phenyl rings that metalate, the phosphorescence profile and radiative rate constants depend considerably on the ancillary ligand.…”

“…Our group has previously outlined strategies to obtain efficient red to NIR (λ em > 600 nm) phosphorescent complexes. , Incorporating nitrogen-containing, electron-rich π-donating ancillary ligands can destabilize the metal-centered HOMO and increase the contribution of the Ir 5 d orbitals to the excited state, leading to augmented k r and Φ PL values. This strategy has produced compounds with Φ PL values as high 0.8 in the red region and 0.5 in the DR-NIR region when 1-phenylisoquinoline (piq) and substituted analogues are used as the cyclometalating (C^N) ligands. , In the course of these previous efforts, we found that the effectiveness of electron-rich ancillary ligands depends on the nature of the C^N ligands. In general, complexes with the electron-rich thiophene-based C^N ligands have photoluminescence properties that vary little as the ancillary ligand is changed, but when C^N ligands have simple phenyl rings that metalate, the phosphorescence profile and radiative rate constants depend considerably on the ancillary ligand. , …”

“…At parity of the ancillary ligand, the E ox values are 110−160 mV more positive when C^N = piqCN, indicating some effect of the electron-withdrawing cyano substituent on the HOMO energy. Compared to previous pphen and piqCN complexes we have described where the electron-rich ancillary ligands are β-ketoiminate, β-diketiminate, and oramidinate derivatives,39 most complexes described here have slightly more positive E ox values and slightly larger electrochemical HOMO− LUMO gaps. DFT Calculations.…”