Lanthanide-Dependent Photochemical and Photophysical Properties of Lanthanide–Anthracene Complexes: Experimental and Theoretical Approaches
Liangliang Wu, Xin‐Da Huang, Weijia Li, Xiaoyan Cao, Wei‐Hai Fang, Li‐Min Zheng, Michael Dolg, Xuebo Chen
Abstract
High Resolution Image Download MS PowerPoint Slide The structural, photophysical, and photochemical properties of Ln(depma)(hmpa) 2 (NO 3 ) 3 (Ln = La, Ce, Nd, Sm, Eu, Tb, Ho, Er, and Yb) complexes 1-Ln were investigated with a multidisciplinary approach involving synthesis, photocycloaddition-based crystal engineering, spectroscopic analytical techniques and quantum chemical ab initio calculations. Depending on the Ln 3+ ion the isostructural 1-Ln complexes exhibit quite different behavior upon excitation at 350–400 nm. Some 1-Ln complexes (Ln = La, Ce, Sm, Tb, Yb) emit a broad and strong band near 533 nm arising from paired anthracene moieties, whereas others (Ln = Nd, Eu, Ho, Er) do not. 1-Eu is not emissive at all, whereas 1-Nd, 1-Ho, and 1-Er exhibit a Ln 3+ based luminescence. Upon irradiation with 365 nm ultraviolet (UV) light 1-Ln (Ln = La, Ce, Sm, Tb, Yb) dimerize by means of a photochemically induced [4 + 4] cycloaddition of the anthracene moieties, whereas 1-Ln (Ln = Nd, Eu, Ho, Er) remain monomers. We propose three models, based on the matching of the energy levels between the Ln 3+ ion and the paired or dimerized anthracene units in the energy-resonance crossing region, as well as on internal conversion-driven and intersystem crossing-driven energy transfer, which explain the Ln 3+ ion regulated photophysics and photochemistry of the 1-Ln complexes.