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

We report the synthesis and characterization of C₂-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 C₂-symmetrical (tpdac)Ln(OTf)₃ complexes in high yields. The tpdac ligands are competent sensitizers for lanthanide luminescence, yielding modest emissions (Φ of ≤28%). Additionally, the complexes exhibit strong circularly polarized luminescence (|g_lum| 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 |g_lum| values and, therefore, should not be overlooked in future studies.