Department of Chemistry, Virginia Tech, 107 Davidson Hall, Blacksburg, Virginia 24061-0212, USA.
Inorg Chem. 2011 Sep 19;50(18):8850-60. doi: 10.1021/ic200793f. Epub 2011 Aug 23.
Five new tetrametallic supramolecules of the motif {(TL)(2)M(dpp)}(2)Ru(BL)PtCl(2) and three new trimetallic light absorbers {(TL)(2)M(dpp)}(2)Ru(BL) (TL = bpy = 2,2'-bipyridine or phen = 1,10-phenanthroline; M = Ru(II) or Os(II); BL = dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis(2-pyridyl)quinoxaline, or bpm = 2,2'-bipyrimidine) were synthesized and their redox, spectroscopic, and photophysical properties investigated. The tetrametallic complexes couple a Pt(II)-based reactive metal center to Ru and/or Os light absorbers through two different polyazine BL to provide structural diversity and interesting resultant properties. The redox potential of the M(II/III) couple is modulated by M variation, with the terminal Ru(II/III) occurring at 1.58-1.61 V and terminal Os(II/III) couples at 1.07-1.18 V versus Ag/AgCl. {(TL)(2)M(dpp)}(2)Ru(BL)(6) display terminal M(dπ)-based highest occupied molecular orbitals (HOMOs) with the dpp(π*)-based lowest unoccupied molecular orbital (LUMO) energy relatively unaffected by the nature of BL. The coupling of Pt to the BL results in orbital inversion with localization of the LUMO on the remote BL in the tetrametallic complexes, providing a lowest energy charge separated (CS) state with an oxidized terminal Ru or Os and spatially separated reduced BL. The complexes {(TL)(2)M(dpp)}(2)Ru(BL) and {(TL)(2)M(dpp)}(2)Ru(BL)PtCl(2) efficiently absorb light throughout the UV and visible regions with intense metal-to-ligand charge transfer (MLCT) transitions in the visible at about 540 nm (M = Ru) and 560 nm (M = Os) (ε ≈ 33,000-42,000 M(-1) cm(-1)) and direct excitation to the spin-forbidden (3)MLCT excited state in the Os complexes about 720 nm. All the trimetallic and tetrametallic Ru-based supramolecular systems emit from the terminal Ru(dπ)→dpp(π*) (3)MLCT state, λ(max)(em) ≈ 750 nm. The tetrametallic systems display complex excited state dynamics with quenching of the (3)MLCT emission at room temperature to populate the lowest-lying (3)CS state population of the emissive (3)MLCT state.
合成了五个新的四金属超分子[{（TL）（2）M（dpp）}（2）Ru（BL）PtCl（2）]（6+）和三个新的三金属光吸收剂[{（TL）（2）M（dpp）}（2）Ru（BL）]（6+）（TL = bpy = 2,2'-联吡啶或 phen = 1,10-菲咯啉；M = Ru（II）或 Os（II）；BL = dpp = 2,3-双（2-吡啶基）吡嗪，dpq = 2,3-双（2-吡啶基）喹喔啉，或 bpm = 2,2'-联嘧啶），并研究了它们的氧化还原、光谱和光物理性质。四金属配合物通过两个不同的多嗪 BL 将基于 Pt（II）的反应性金属中心与 Ru 和/或 Os 光吸收剂偶联，提供结构多样性和有趣的性质。M（II/III）对的氧化还原电位通过 M 的变化进行调节，末端 Ru（II/III）的氧化还原电位为 1.58-1.61 V，末端 Os（II/III）的氧化还原电位为 1.07-1.18 V 相对于 Ag/AgCl。[{（TL）（2）M（dpp）}（2）Ru（BL）]（PF（6））（6）显示基于 M（dπ）的末端 M（dπ）-基于最高占据分子轨道（HOMO），而基于 dpp（π*）的最低未占据分子轨道（LUMO）能量相对不受 BL 性质的影响。Pt 与 BL 的偶联导致轨道反转，四金属配合物中 LUMO 定域在远程 BL 上，提供具有氧化端 Ru 或 Os 和空间分离的还原 BL 的最低能量电荷分离（CS）状态。配合物[{（TL）（2）M（dpp）}（2）Ru（BL）]（6+）和[{（TL）（2）M（dpp）}（2）Ru（BL）PtCl（2）]（6+）通过在 540nm（M = Ru）和 560nm（M = Os）处的强烈金属-配体电荷转移（MLCT）跃迁在整个 UV 和可见区域中有效地吸收光（ε≈33,000-42,000 M（-1）cm（-1））和在 Os 配合物中直接激发到自旋禁戒的（3）MLCT 激发态约 720nm。所有基于三价 Ru 的超分子系统都从末端 Ru（dπ）→dpp（π*）（3）MLCT 状态发射，λ（max）（em）≈750nm。四金属系统显示出复杂的激发态动力学，在室温下通过猝灭（3）MLCT 发射来填充发射（3）MLCT 状态的最低能（3）CS 态。
