Circularly Polarized Luminescence from Enantiopure <i>C</i><sub>2</sub>-Symmetrical Tetrakis(2-pyridylmethyl)-1,2-diaminocyclohexane Lanthanide Complexes
Kaitlynn M. Ayers, Nathan D. Schley, Gaël Ung
Abstract
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 (|glum| 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 |glum| values and, therefore, should not be overlooked in future studies.