Two chiral EuIII and SmIII enantiomeric pairs with enantiopure N-donor ligands: showing strong third-harmonic generation and photoluminescence properties

Abstract

The reaction of the precursors Eu(dbm)₃(H₂O) and Sm(dbm)₃(H₂O) with enantiopure monobidentate N-donor ligands (L_R/L_S), respectively, afforded two chiral Eu^III and Sm^III enantiomeric pairs, namely Ln(dbm)₃(L_R)/Ln(dbm)₃(L_S) (Ln = Eu^III, D-1/L-1 and Ln = Sm^III, D-2/L-2), where dbm⁻ = dibenzoylmethanate and L_R/L_S = (−)/(+)-4,5-pinenepyridyl-2-pyrazine. Compared with their precursors, D-1 and D-2 display highly enhanced photophysical properties under excitation with visible light. A study of nonlinear optical (NLO) response reveals that Eu(dbm)₃(H₂O) and Sm(dbm)₃(H₂O) only show moderate second-harmonic generation (SHG) responses, while D-1/L-1 and D-2/L-2 only exhibit strong third-harmonic generation (THG) responses. The THG intensities of D-1/L-1 and D-2/L-2 are 62/59 and 56/58 × α-SiO₂, respectively. These findings clearly indicate that introducing L_R and L_S into Eu(dbm)₃(H₂O) and Sm(dbm)₃(H₂O) can not only highly boost the photophysical performances but also lead to the switching of the NLO responses from SHG to THG.