The triplet excited state of a new Ir-based photosensitizer with two chromenopyridinone and one bipyridine-based ligands has been studied by pump–probe X-ray absorption near edge structure (XANES) spectroscopy coupled with DFT calculations. The excited state has a lifetime of 0.5 μs in acetonitrile and is characterized by very small changes of the local atomic structure with an average metal–ligand bond length change of less than 0.01 Å. DFT-based calculations allow the interpretation of the XANES in the energy range of ∼50 eV around the absorption edge. The observed transient XANES signal arises from an additional metal-centered Ir 5d vacancy in the excited state which appears as a result of electron transfer from the metal to the ligand. The overall energy shift of the excited state spectrum originates from the shift of 2p and unoccupied states induced by screening effects. The approach for the analysis of time-resolved spectra of 5d metal complexes is quite general and can also be used if excited and ground state structures are significantly different.

中文翻译：

---

用泵-探针XAS研究含铬吡啶并酮配体的Ir光敏剂的三重态†

通过泵浦探针X射线吸收近边缘结构（XANES）光谱和DFT计算，研究了一种新的基于Ir的光敏剂的三重激发态，该光敏剂具有两个色胺吡啶酮和一个联吡啶基配体。激发态在乙腈中的寿命为0.5μs，其特征是局部原子结构的变化很小，平均金属-配体键长变化小于0.01Å。基于DFT的计算可以解释XANES在约50 eV的吸收边缘附近的能量范围内。观察到的瞬态XANES信号是由于处于激发态的另一个以金属为中心的Ir 5d空位产生的，该空位是由于电子从金属转移到配体而产生的。激发态谱的总能量位移源于2p的位移和屏蔽效应引起的未占据态。5d金属配合物的时间分辨光谱分析方法非常通用，如果激发态和基态结构明显不同，也可以使用该方法。