σ‑Pt-BODIPY Complexes with Platinum Attachment to Carbon Atoms C2 or C3: Spectroscopic, Structural, and (Spectro)Electrochemical Studies and Photocatalysis

In this work we discuss five new complexes with the general formula trans-Pt­(bodipy)­I­(PEt3)2, where differently substituted bodipy dyes attach to the coordination center via a direct Pt–C σ-bond to the pyrrolic carbon atom C2 or C3. We also report an isolable intermediate of the oxidative addition step where the bodipy is η2-bonded to the cis-Pt­(0)­(PEt3)2 moiety. Comparison between the new complexes, meso-platinated analogue 8-Pt, and the parent dyes reveals that the site of platinum attachment influences the spectroscopic, photophysical, electrochemical, and electronic properties. In contrast to 8-Pt, absorption and emission bands are red-shifted with respect to the parent dyes. 2-Platinated bodipy dyes 2-Pt-6H, 2-Pt-6I, 2-Pt-Mes-6I, and 2-Pt-6Et exhibit dual fluorescence and NIR phosphorescence emissions, with low quantum yields, whereas 3-Pt emits solely by fluorescence (ΦFl = 52.7%). The complexes are modestly efficient sensitizers for photochemical 1O2 production but outperform methylene blue. They also undergo one reversible one-electron reduction and oxidation as indicated by cyclic voltammetry. Half-wave potentials are cathodically shifted by 340–510 mV with respect to the parent dyes. The one-electron reduced and some of the one-electron oxidized forms were generated and investigated by UV/vis/NIR and EPR spectroscopy as well as TD-DFT calculations. The similarity of their spectra to those of the one-electron reduced or oxidized forms of other bodipy dyes as well as the richly structured EPR spectra and g-values close to ge attest to a dominant bodipy character of the relevant frontier MOs.

本工作探讨了5种通式为trans-Pt(bodipy)I(PEt₃)₂的新型配合物，其中不同取代的氟化硼二吡咯（bodipy）染料通过Pt与吡咯环碳原子C2或C3之间的直接Pt–C σ键与配位中心结合。本研究还报道了氧化加成步骤中一种可分离的中间体，该中间体中bodipy以η²配位键与cis-Pt(0)(PEt₃)₂结构片段结合。通过对比新型配合物、中位铂修饰的类似物8-Pt以及母体染料，发现铂原子的结合位点会对其光谱、光物理、电化学及电子性质产生影响。与8-Pt不同，这些配合物的吸收与发射峰相较于母体染料发生了红移。2位铂修饰的bodipy染料2-Pt-6H、2-Pt-6I、2-Pt-Mes-6I及2-Pt-6Et展现出双荧光发射与近红外（NIR）磷光发射，且量子产率较低；而3-Pt仅通过荧光发射（荧光量子产率ΦFl = 52.7%）。该类配合物作为光化学单线态氧（¹O₂）生成的敏化剂效率中等，但性能优于亚甲基蓝。循环伏安测试表明，这类配合物可发生一次可逆的单电子还原与氧化反应。相较于母体染料，其半波电位向阴极方向偏移了340~510 mV。通过紫外-可见-近红外（UV/vis/NIR）光谱、电子顺磁共振（EPR）光谱以及含时密度泛函理论（TD-DFT）计算，对单电子还原产物与部分单电子氧化产物进行了制备与表征。这些产物的光谱与其他bodipy染料的单电子还原或氧化产物的光谱相似，且其EPR光谱结构丰富、g值接近自由电子的g因子gₑ，证明相关前线分子轨道（frontier MOs）主要具有bodipy的电子特性。