Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, England, U.K.
Inorg Chem. 2023 Feb 13;62(6):2793-2805. doi: 10.1021/acs.inorgchem.2c03934. Epub 2023 Jan 27.
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)(acac) complexes (where ppy is the 2-phenylpyridyl chelate and acac is the acetylacetonate chelate) with an oligo(-phenyleneethynylene) (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)(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)(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)(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)(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 (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 MLCT states of many Ir(ppy)(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.
具有长发射寿命（微秒到毫秒）的发射性化合物在一系列应用中很有意义，从氧气传感到细胞成像。本文研究了具有寡聚（苯乙炔）（OPE3）基序的 Ir(ppy)(acac) 配合物（其中 ppy 是 2-苯基吡啶螯合物，acac 是乙酰丙酮螯合物）的发射行为，其中 OPE3 基序连接到 acac 或 ppy 的三个对位环和两个乙炔桥。由于可以获得长寿命的 OPE3 三重态，因此研究了具有长寿命 OPE3 三重态的 Ir(ppy)(acac) 配合物。合成了九个带有 OPE3 单元的 Ir(ppy)(acac) 配合物，其中 OPE3 基序位于 acac 部分（aOPE3），位于 ppy 螯合物中（pOPE3）或通过 durylene 连接物连接到 ppy（dOPE3）。aOPE3 和 dOPE3 配合物中的 OPE3 单元通过采用垂直的环环取向与 Ir(ppy)(acac) 核心解耦，而 pOPE3 配合物中的 OPE3 整合到 ppy 配体中，以最大限度地与 Ir(ppy)(acac) 核心进行电子耦合。虽然共轭的 pOPE3 配合物显示出 0.69-32.8 μs 的发射寿命，类似于此处合成的非-OPE3 Ir(ppy)(acac) 配合物的 1.00-23.1 μs 的发射寿命，但解耦的 aOPE3 和 dOPE3 配合物则显示出 50-625 μs 的长发射寿命。aOPE3 和 dOPE3 配合物中发现的长寿命归因于分子内可逆电子能量转移（REET），其中长寿命三重态金属到配体电荷转移（MLCT）态通过 REET 与甚至更长寿命的三重态局域 OPE3 态交换。从 aOPE3 和 dOPE3 配合物的激发波长依赖性和时间依赖性发射光谱中观察到的变化支持了所提出的 REET 过程，而 pOPE3 配合物的发射光谱由于许多 Ir(ppy)(acac) 配合物的稳定 MLCT 态而独立于激发波长和时间。dOPE3 配合物的长寿命、可见发射最大值（524-526nm）和 0.44-0.60 的光致发光量子产率表明，此类化合物有可能在氧气传感和细胞成像应用中得到利用。
