Promoting a Significant Increase in the PhotoluminescenceQuantum Yield of Terbium(III) Complexes by Ligand Modification

Two discrete mononuclear complexes, [Tb(bbpen)(NO3)] (I) and [Tb(bbppn)(NO3)] (II), for which H2bbpen = N,N′-bis(2-hydroxybenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine and H2bbppn = N,N′-bis(2-hydroxylbenzyl)-N,N’-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by FTIR, Raman, and photoluminescence (PL, steady-state and time-resolved modes) spectroscopy. The attachment of a methyl group to the ethylenediamine portion of the ligand backbone differentiates II from I and acts as a determining feature to both the structural and optical properties of the former. The single-crystal X-ray structure of H2bbppn is described here for the first time, while that of complex II has been redetermined in the monoclinic C2 space group in light of new diffraction data. In II, selective crystallization leads to spontaneous resolution of enantiomeric molecules in different crystals. Absolute emission quantum yields (ϕ) and luminescence excited-state lifetimes (at room temperature and 11 K...