Synthesis of Panchromatic Ru(II) Thienyl-Dipyrrin Complexes and Evaluation of Their Light-Harvesting Capacity

Ru­(II) complexes with 5-(3-thienyl)-4,6-dipyrrin (3-TDP), containing 2,2′-bipyridine (bpy) or 4,4′-bis­(methoxycarbonyl)-2,2′-bipyridine (dcmb) as coligands, have been prepared and extensively characterized. Crystal structure determination of [Ru­(bpy)2(3-TDP)]­PF6 (1a) and [Ru­(bpy)­(3-TDP)2] (2) reveals that the 3-thienyl substituent is rotated with respect to the plane of the dipyrrinato moiety. These complexes, as well as [Ru­(dcmb)2(3-TDP)]­PF6 (1b), act as panchromatic light absorbers in the visible range, with two strong absorption bands observable in each case. A comparison to known Ru­(II) complexes and quantum-chemical calculations at the density functional theory (DFT) level indicate that the lower-energy band is due to metal-to-ligand charge transfer (MLCT) excitation, although the frontier occupied metal-based molecular orbitals (MOs) contain significant contributions from the 3-TDP moiety. The higher energy band is assigned to the π–π* transition of the 3-TDP ligand. Each complex exhibits an easily accessible one-electron oxidation. According to DFT calculations and spectroelectrochemical experiments, the first oxidation takes place at the RuII center in 1a, but is shifted to the 3-TDP ligand in 1b. An analysis of MO energy diagrams suggests that complex 1b has potential to be used for light harvesting in the dye-sensitized (Grätzel) solar cell.

以5-(3-噻吩基)-4,6-二吡咯啉（3-TDP）为配体、以2,2′-联吡啶（bpy）或4,4′-双(甲氧羰基)-2,2′-联吡啶（dcmb）为辅助配体的二价钌配合物已被合成并进行了全面表征。对[二(2,2′-联吡啶)(3-TDP)合钌(II)]六氟磷酸盐（1a）和[单(2,2′-联吡啶)二(3-TDP)合钌(II)]（2）的晶体结构解析表明，3-噻吩基取代基相对于二吡咯啉阴离子基团的平面发生了扭转。这些配合物以及[二(4,4′-双(甲氧羰基)-2,2′-联吡啶)(3-TDP)合钌(II)]六氟磷酸盐（1b）均可在可见光区实现全光谱光吸收，且每种配合物均呈现两个强吸收带。与已知二价钌配合物的对比以及密度泛函理论（DFT）水平下的量子化学计算结果显示，低能吸收带源于金属到配体电荷转移（MLCT）激发，尽管占据型前线金属基分子轨道（MOs）中包含来自3-TDP基团的显著贡献。高能吸收带则被归因为3-TDP配体的π-π*跃迁。每种配合物均表现出易于发生的单电子氧化过程。根据DFT计算与光谱电化学实验结果，1a中的首次氧化发生在Ru(II)中心，而1b中的氧化位点则转移至3-TDP配体。对分子轨道能级图的分析表明，配合物1b具备应用于染料敏化（格拉策尔）太阳能电池光捕获材料的潜力。