Circularly Polarized Luminescence from Enantiopure C2-Symmetrical Tetrakis(2-pyridylmethyl)-1,2-diaminocyclohexane Lanthanide Complexes

Abstract

We report the synthesis and characterization of C-2-symmetrical lanthanide complexes supported by enantiopure hexadentate ligands derived from 1,2-diaminocyclohexane. Coordination of (R,R)- or (S,S)-N,N,N',N'-tetrakis(2-pyridylmethyl) -trans- 1,2-diaminocyclohexane (tpdac) to samarium, europium, terbium, and dysprosium generates the corresponding C-2-symmetrical (tpdac)Ln(OTf)(3) complexes in high yields. The tpdac ligands are competent sensitizers for lanthanide luminescence, yielding modest emissions (Phi of <= 28%). Additionally, the complexes exhibit strong circularly polarized luminescence (vertical bar g(lum)vertical bar values of up to 0.13, 0.09, 0.22, and 0.15 for Sm, Eu, Tb, and Dy, respectively) in solution. We also observed that some transitions typically associated with small dissymmetry factors exhibit unusually high vertical bar g(lum)vertical bar values and, therefore, should not be overlooked in future studies.