Two chiral lanthanide PrIII and HoIII complexes: NIR luminescence and nonlinear optical properties

Abstract

Employing a chiral N∧N-donor ligand (−)-4,5-pinene-2,2′-bipyridine (L) to react with Pr(dbm)₃(H₂O) and Ho(dbm)₃(H₂O), respectively, two chiral mononuclear lanthanide (Ln^III) complexes with the formula [Ln(dbm)₃(L)] [Ln = Pr (1) and Ho (2)] were obtained, in which dbm⁻ = dibenzoylmethanate. Investigation on their photoluminescence properties reveals that 1 and 2 display characteristic near-infrared (NIR) emissions of Pr^III and Ho^III ions upon excitation with visible light (410 nm), respectively. More notably, study on their nonlinear optical (NLO) responses unveils that 1 and 2 not only present second-harmonic generation (SHG) responses due to their noncentrosymmetric molecular structures, but also exhibit strong third-harmonic generation (THG) responses simultaneously. THG intensities of 1 and 2 are 46.7 and 66.5 × α-SiO₂, respectively, which are outstanding among the reported THG-active mononuclear Ln^III complexes. 1 and 2 represent the first examples of Ln^III complexes not only showing NIR luminescence but also displaying simultaneous SHG and THG responses.