Tuning Emission Lifetimes of Ir(C^N)₂(acac) Complexes with Oligo(phenyleneethynylene) Groups

Abstract

Emissive compounds with long emission lifetimes (μs to ms) in the visible region are of interest for a range of applications, from oxygen sensing to cellular imaging. The emission behavior of Ir(ppy) 2 (acac) complexes (where ppy is the 2-phenylpyridyl chelate and acac is the acetylacetonate chelate) with an oligo(paraphenyleneethynylene) (OPE3) motif containing three para-rings and two ethynyl bridges attached to acac or ppy is examined here due to the accessibility of the long-lived OPE3 triplet states. Nine Ir(ppy) 2 (acac) complexes with OPE3 units are synthesized where the OPE3 motif is at the acac moiety (aOPE3), incorporated in the ppy chelate (pOPE3) or attached to ppy via a durylene link (dOPE3). The aOPE3 and dOPE3 complexes contain OPE3 units that are decoupled from the Ir(ppy) 2 (acac) core by adopting perpendicular ring−ring orientations, whereas the pOPE3 complexes have OPE3 integrated into the ppy ligand to maximize electronic coupling with the Ir(ppy) 2 (acac) core. While the conjugated pOPE3 complexes show emission lifetimes of 0.69−32.8 μs similar to the lifetimes of 1.00−23.1 μs for the non-OPE3 Ir(ppy) 2 (acac) complexes synthesized here, the decoupled aOPE3 and dOPE3 complexes reveal long emission lifetimes of 50−625 μs. The long lifetimes found in aOPE3 and dOPE3 complexes are due to intramolecular reversible electronic energy transfer (REET) where the long-lived triplet-state metal to ligand charge transfer ( 3 MLCT) states exchange via REET with the even longer-lived triplet-state localized OPE3 states. The proposed REET process is supported by changes observed in excitation wavelength-dependent and time-dependent emission spectra from aOPE3 and dOPE3 complexes, whereas emission spectra from pOPE3 complexes remain independent of the excitation wavelength and time due to the well-established 3 MLCT states of many Ir(ppy) 2 (acac) complexes. The long lifetimes, visible emission maxima (524−526 nm), and photoluminescent quantum yields of 0.44−0.60 for the dOPE3 complexes indicate the possibility of utilizing such compounds in oxygen-sensing and cellular imaging applications.

Metal–Organic Bichromophore Lowers the Upconversion Excitation Power Threshold and Promotes UV Photoreactions

“…Pyrene is a well-suited triplet reservoir for Ru II polypyridine complexes with triplet energies around 2.1 eV, − but when aiming at blue-to-UV upconversion, a higher triplet energy is advantageous. Cyclometalated Ir III complexes such as Ir ref (Figure a) fulfill this requirement with triplet energies near 2.7 eV, , but this calls for a different triplet reservoir. − Naphthalene ( Naph ) was identified as an energetically matching partner to obtain a substantially longer-lived triplet state in the bichromophore of Figure b ( Ir Naph ) . At the same time, all benefits offered by the Ir III complex remain exploitable, in particular, its absorption tailing into the blue spectral range, high photostability, and high efficiency for intersystem crossing.…”

Aggregation-induced emission of cyclometalated rhodium(iii) and iridium(iii) phenylpyridine complexes with ancillary 1,3-diketones

“…The shapes of the spectra are practically invariant to the replacement of the methyl group by the phenyl ring, but the introduction of the trifluoromethyl group causes a noticeable change in the spectra irrespective of the aromatic ring in the β-diketonate (phenyl or 2-thienyl). Complexes Ir2–Ir4 possess almost identical single-band luminescence spectra similar to that of [Ir(ppy) 2 acac] 67 (acac = acetylacetone), indicating that these complexes have the same triplet-excited state localized mainly at the cyclometalated fragment Ir(ppy) 2 + . The aromatic ring in the diketonate significantly reduces the quantum yields of the complexes compared with that of [Ir(ppy) 2 acac] because of a high probability of the nonradiative deactivation of the excited state caused by the rotation of the ring(s), 68 whereas the variation of substituents has only a marginal effect on emission, which agrees with literature data.…”

Machine Learning Algorithm for Artificial Intelligence-Based Precise Structural Modeling in Organic Light-Emitting Diodes

“…Four HTLs with a constant thickness pair of 45 and 90 nm were used based on the optimized OLED structure shown in Figure . Decreasing the n led to broader emission spectra due to increased light scattering and diffraction within the layer. − Figure b provides a closer look at the affected region in the emission spectra, and it becomes evident that the device employing TAPC best matches the PL, falling within the error margin. On the other hand, devices using poly-TPD, CBP, and TCTA show a trend of increased emission area as the refractive index decreases.…”