Origin of the initial charge separation in optically-excited Ruthenium(II) tris(bidentate) complexes of intrinsic D₃ symmetry has remained a disputed issue for decades. Here we measure the femtosecond two-photon absorption (2PA) cross section spectra of [Ru(2,2′-bipyridine)₃]² and [Ru(1,10-phenanthroline)₃]² in a series of solvents with varying polarity and show that for vertical transitions to the lower-energy ¹MLCT excited state, the permanent electric dipole moment change is nearly solvent-independent, Δμ = 5.1–6.3 D and 5.3–5.9 D, respectively. Comparison of experimental results with quantum-chemical calculations of complexes in the gas phase, in a polarizable dielectric continuum and in solute-solvent clusters containing up to 18 explicit solvent molecules indicate that the non-vanishing permanent dipole moment change in the nominally double-degenerate E-symmetry state is caused by the solute-solvent interaction twisting the two constituent dipoles out of their original opposite orientation, with average angles matching the experimental two-photon polarization ratio.

几十年来，固有D ₃对称性的光激发钌（II）三（双齿）配合物中的初始电荷分离的起源一直是一个有争议的问题。在这里，我们在一系列极性不同的溶剂中测量了[Ru（2,2'-联吡啶）₃ ] ²和[Ru（1,10-菲咯啉）₃ ] ²的飞秒双光子吸收（2PA）截面光谱并且表明，对于垂直转变到较低能量¹ MLCT激发态，永久电偶极矩的变化几乎是溶剂无关的，Δ μ 分别为5.1–6.3 D和5.3–5.9D。在气相，可极化的介电连续体和包含多达18个显式溶剂分子的溶质-溶剂簇中，对配合物的量子化学计算进行的实验结果比较表明，名义上双简并的永久偶极矩变化不变。电子对称状态是由于溶质与溶剂的相互作用将两个组成的偶极子扭转出其原始的相反方向而引起的，其平均角度与实验的双光子极化比相匹配。