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.