Near infra-red emitting Ru(<scp>ii</scp>) complexes of tridentate ligands: electrochemical and photophysical consequences of a strong donor ligand with large bite angles
作者:Amlan K. Pal、Scolastica Serroni、Nelsi Zaccheroni、Sebastiano Campagna、Garry S. Hanan
DOI:10.1039/c4sc01604a
日期:——
A novel N^N^N tridentate ligand dgpy (dgpy = 2,6-diguanidylpyridine) was synthesized by a Pd-catalyzed C–N bond-forming reaction. A novel family of [RuII(tpy')(dgpy)](PF6)2 (1 and 2) or [RuII(dpt')(dgpy)](PF6)2 (3 and 4) (tpy' = substituted-2,2′:6′,2′-terpyridine, dpt' = substituted-2,4-dipyrid-2′-yl-1,3,5-triazine) complexes are reported. The dgpy ligand (80%) and the heteroleptic complexes 1–4 (37–60%) were obtained in modest to good yields. The dgpy ligand and its complexes were fully characterized by a variety of techniques including X-ray crystallography and density functional theory (DFT). In cyclic voltammetric studies, the complexes exhibit a RuIII/II couple, which is 600–800 mV less positive than the RuIII/II couple in [Ru(tpy)2]2+. The 1MLCT absorption maxima of all the complexes (620–740 nm) are considerably red-shifted as compared to that of [Ru(tpy)2]2+ (474 nm). The 3MLCT emission maxima of complexes 1 and 2 are also red-shifted by about 270 nm compared to that of [Ru(tpy)2]2+ (629 nm) at room temperature (298 K), whereas the corresponding maxima for complexes 3 and 4 are shifted by about 330 nm at 77 K. The relative trends in redox potentials and 1MLCT maxima are in good agreement with DFT and TD-DFT calculations. Complexes 1 and 2 emit from a RuII-to-tpy 3MLCT state, which is rarely the emitting state at λ > 850 nm in [Ru(tpy)(N^N^N)]2+ complexes when the ancillary ligand is neutral. Complexes 1 and 2 also exhibit long excited-state lifetimes (τ ∼ 100 ns) at room temperature with associated quantum yield (Φ) of 0.001. The reported τ and Φ values are approximately 400–500 times and 1000 times higher compared to those of [Ru(tpy)2]2+ (τ = 0.25 ns, Φ ≤ 5 × 10−6), respectively. Complexes 3 and 4 emit from a RuII-to-dpt 3MLCT state, albeit only at 77 K (τ = 0.25 ns) due to rapid deactivation of their 3MLCT state according to the energy-gap law. The improved photophysical properties of the complexes are consequences of enlarged separation of the 3MLCT–3MC states, due to the strong donation and larger bite angles of the dgpy ligand.
一种新型的N^N^N三齿配体dgpy(dgpy = 2,6-二氨基吡啶)通过Pd催化的C–N键形成反应合成。报道了一类新型的[RuII(tpy')(dgpy)](PF6)2(1和2)或[RuII(dpt')(dgpy)](PF6)2(3和4)(tpy' = 替代-2,2′:6′,2′-萜吡啶,dpt' = 替代-2,4-二吡啶-2′-基-1,3,5-三嗪)复合物。dgpy配体(80%)和异配体复合物1–4(37–60%)的产率中等到良好。利用多种技术对dgpy配体及其复合物进行了全面表征,包括X射线晶体学和密度泛函理论(DFT)。在循环伏安研究中,这些复合物展示了RuIII/II对,电位比[Ru(tpy)2]2+中的RuIII/II对降低了600–800毫伏。所有复合物的1MLCT吸收最大值(620–740 nm)相较于[Ru(tpy)2]2+(474 nm)显著红移。复合物1和2的3MLCT发射最大值在室温(298 K)下也相比[Ru(tpy)2]2+(629 nm)红移了约270 nm,而复合物3和4在77 K下的对应最大值则红移约330 nm。氧化还原电位和1MLCT最大值的相对趋势与DFT和TD-DFT计算结果较为一致。复合物1和2从RuII到tpy的3MLCT态发射,这在伴随配体为中性时的[Ru(tpy)(N^N^N)]2+复合物中较为少见,且λ > 850 nm时发射状态的出现较为罕见。复合物1和2在室温下呈现长的激发态寿命(τ ∼ 100 ns),伴随的量子产率(Φ)为0.001。报告的τ和Φ值分别约比[Ru(tpy)2]2+(τ = 0.25 ns,Φ ≤ 5 × 10−6)高出400–500倍和1000倍。复合物3和4仅在77 K下从RuII到dpt的3MLCT态发射(τ = 0.25 ns),这是因为根据能隙法,它们的3MLCT态迅速非辐射性去活化。复合物的光物理特性改善是由于dgpy配体的强供体效应和更大的咬合角导致3MLCT–3MC态的分离增大。