Enhanced Electric Dipole Transition in Lanthanide Complex with Organometallic Ruthenocene Units

Enhanced luminescence of a lanthanide complex with dynamic polarization of the excited state and molecular motion is introduced. The luminescent lanthanide complex is composed of one Eu­(hfa)3 (hfa, hexafluoroacetylacetonate) and two phosphine oxide ligands with ruthenocenyl units Rc, [Eu­(hfa)3(RcPO)2] (RcPO = diphenylphosphorylruthenocene). The ruthenocenyl units in the phosphine oxide ligands play an important role of switching for dynamic molecular polarization and motion in liquid media. The oxidation states of the ruthenocenyl unit (Rc­(1+)/Rc­(1+)) are controlled by potentiostatic polarization. Eu­(III) complexes attached with bidentate phosphine oxide ligands containing ruthenocenyl units, [Eu­(hfa)3(RcBPO)] (RcBPO = 1,1′-bis­(diphenylphosphoryl)­ruthenocene), and with bidentate phosphine oxide ligands, [Eu­(hfa)3(BIPHEPO)] (BIPHEPO =1,1′-biphenyl-2,2′-diylbis­(diphenylphosphine oxide), were also prepared as references. The coordination structures and electrochemical properties were analyzed using single crystal X-ray analysis, cyclic voltammetry, and absorption spectroscopy measurements. The luminescence properties were estimated using an optoelectrochemical cell. Under potentiostatic polarization, a significant enhancement of luminescence was successfully observed for [Eu­(hfa)3(RcPO)2], while no spectral change was observed for [Eu­(hfa)3(RcBPO)]. In this study, the remarkable enhanced luminescence phenomena of Eu­(III) complex based on the dynamic molecular motion under potentiostatic polarization have been performed.

本研究报道了一类兼具激发态动态极化与分子运动特性的镧系配合物（lanthanide complex）的发光增强效应。该发光镧系配合物由1个三(六氟乙酰丙酮)合铕(III) [Eu(hfa)₃，其中hfa为hexafluoroacetylacetonate，六氟乙酰丙酮根]与2个带有二茂钌基单元（ruthenocenyl units）的氧化膦配体（phosphine oxide ligands）配位而成，具体化学式为[Eu(hfa)₃(RcPO)₂]（RcPO = diphenylphosphorylruthenocene，二苯膦酰基二茂钌）。该氧化膦配体中的二茂钌基单元，在液相介质中可作为动态分子极化与运动的调控开关，发挥关键作用。二茂钌基单元的氧化态[Rc(1+)/Rc(1+)]可通过恒电位极化（potentiostatic polarization）进行精准调控。本研究同时合成了两类参比配合物：一类为带有含二茂钌基单元的双齿氧化膦配体（bidentate phosphine oxide ligands）的铕(III)配合物[Eu(hfa)₃(RcBPO)]（RcBPO = 1,1′-bis(diphenylphosphoryl)ruthenocene，1,1′-双(二苯膦酰基)二茂钌），另一类为仅带有双齿氧化膦配体的铕(III)配合物[Eu(hfa)₃(BIPHEPO)]（BIPHEPO = 1,1′-biphenyl-2,2′-diylbis(diphenylphosphine oxide)，1,1′-联苯-2,2′-二基双(二苯基膦氧化物)）。研究通过单晶X射线分析（single crystal X-ray analysis）、循环伏安法（cyclic voltammetry）与吸收光谱（absorption spectroscopy）测试，对上述配合物的配位结构与电化学性能进行了表征分析。采用光电化学池（optoelectrochemical cell）对各配合物的发光性能进行了测试评估。在恒电位极化条件下，[Eu(hfa)₃(RcPO)₂]的发光强度出现了显著增强，而参比配合物[Eu(hfa)₃(RcBPO)]未观测到任何光谱变化。本研究针对恒电位极化下基于动态分子运动的铕(III)配合物显著发光增强现象开展了系统研究。