ELECTRONIC-STRUCTURE OF THE MOLECULAR LIGHT SWITCH [RU(BPY)2(DPPZ)]2+ (DPPZ = DIPYRIDO[3,2-A-2',3'-C]PHENAZINE) - CYCLIC VOLTAMMETRIC, UV VIS, AND EPR ENDOR STUDY OF MULTIPLY REDUCED COMPLEXES AND LIGANDS
ELECTRONIC-STRUCTURE OF THE MOLECULAR LIGHT SWITCH [RU(BPY)2(DPPZ)]2+ (DPPZ = DIPYRIDO[3,2-A-2',3'-C]PHENAZINE) - CYCLIC VOLTAMMETRIC, UV VIS, AND EPR ENDOR STUDY OF MULTIPLY REDUCED COMPLEXES AND LIGANDS
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DOI：
10.1021/ic00054a009
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发表时间：
1993-01-20
影响因子：
4.6
通讯作者：
ZALIS, S
中科院分区：
文献类型：
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作者：
FEES, J;KAIM, W;ZALIS, S
用低温循环伏安法、紫外/维斯光谱和电子顺磁共振谱研究了双吡啶并[3，2-a：2 '，3'-c]吩嗪（dppz）及其11，12-二甲基衍生物dmdppz和相应的[Ru（bpy）2]2+配合物的多重还原态。（dm）dppz配体在两个可逆的步骤中被还原，然后是对水分非常敏感的第三步。得到了中间体阴离子自由基的高分辨EPR谱和H-1-ENDOR谱。结果解释使用HMO/McLachlan微扰方法的π自旋人口和轨道能量。三个低位未占据的π分子轨道可以被鉴定为吩嗪型（b1，最低）和α-二亚胺部分的psi（b1）和chi（a2）轨道。配合物与N（4），N（5）-结合的[Ru（bpy）2]2+片段显示至少6个可逆的单电子还原步骤在严格干燥的DMF中在200 K;前四个持久的还原态的EPR和UV/维斯光谱进行了表征。的前三个还原态的复合物的EPR光谱显示的信号，这证明了占用吩嗪本地化的π * 轨道（DM）dppz由一个单一的电子，逐步减少的bpy配体导致的EPR信号的强度随温度变化的损失。非常碱性的四重还原态表现出EPR特征，这对于Ru（II）结合的α-二亚胺阴离子自由基来说是典型的。所有的归属都得到了紫外/维斯光谱和氧化还原电位值分析的支持。由于非常容易质子化的较高还原态对于EPR和UV/维斯表征而言不足够持久，因此进一步的分配可以仅基于氧化还原电位值的分析。具有不同氧化还原和“光学"轨道的复合物的特定复合电子结构与它们的”光开关“行为有关，即与在非水环境中不存在发光猝灭有关。
The chelate ligand dipyrido[3,2-a:2',3'-c]phenazine(dppz), its 11,12-dimethyl derivative dmdppz, and corresponding complexes with [Ru(bpy)2]2+ were studied in multiply reduced states by low-temperature cyclic voltammetry and UV/vis and EPR spectroscopy. The (dm)dppz ligands are reduced in two reversible steps, followed by a very moisture-sensitive third step. Highly resolved EPR and H-1-ENDOR spectra of the intermediate anion radicals were obtained and analyzed. The results are interpreted using a HMO/McLachlan perturbation approach of pi spin populations and orbital energies. Three low-lying unoccupied pi molecular orbitals can be identified as phenazine-type (b1, lowest) and as the psi(b1) and chi(a2) orbitals of the alpha-diimine moiety. Complexes with the N(4),N(5)-bound [Ru(bpy)2]2+ fragment show at least six reversible one-electron reduction steps in rigorously dried DMF at 200 K; the first four persistent reduced states were characterized by EPR and UV/vis spectroscopy. The EPR spectra of the first three reduced states of the complexes show a signal which proves the occupation of the phenazine-localized pi* orbital of (dm)dppz by a single electron, the stepwise reduction of the bpy ligands resulting in temperature-dependent intensity loss of that EPR signal. The very basic quadruply reduced state exhibits EPR characteristics which are typical for Ru(II)-bound alpha-diimine anion radicals. All assignments are supported by UV/vis spectra and analyses of redox potential values. Because the very easily protonated higher reduced states are not sufficiently persistent for EPR and UV/vis characterization, further assignments could thus be based only on the analysis of redox potential values. The particular composite electronic structure of the complexes with differing redox and ''optical'' orbitals is related to their ''light switch'' behavior, i.e. to the absence of luminescence quenching in a nonaqueous environment.