Solvent dependence of the optical activity associated with tris(DD-dicampholylmethanato)europium(III)

Abstract

Circularly polarized luminescence (c.p.l.) spectroscopy has been used to study the optical activity of the title complex dissolved in 40 different solvents. The solvents ranged from being non-co-ordinating in nature (CHCl₃ or CCl₄) to being strongly co-ordinative toward the Eu^III ion (phosphate esters, amines, N-substituted amines, formamide and acetamide derivatives, alcohols, and ketones). Strong optical activity could be observed within the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ Eu^III transitions in almost every case. Two basic c.p.l. lineshapes were found to exist, and many solvents were found in which both patterns were observed to superimpose. The plausible stereochemistries of the [Eu(dcm)₃(S)₂](dcm =DD-dicampholylmethanate, S = substrate) adduct complex were examined in order to understand the nature of the observed chiroptical spectra. A variety of geometrical and enantiomeric isomerism accounted for the observed trends.