Two pairs of chiral YbIII enantiomers presenting distinct NIR luminescence and circularly polarized luminescence performances with giant differences in second-harmonic generation responses

Abstract

By introducing enantiomerically pure mono-bidentate N-donor ligands (L_R/L_S) into Yb(btfa)₃(H₂O)₂ and Yb(dbm)₃(H₂O), respectively, two pairs of chiral Yb^III enantiomers, namely Yb(btfa)₃L_R/Yb(btfa)₃L_S (D-1/L-1) and [Yb(dbm)₃L_R]·[Yb(dbm)₃(C₂H₅OH)]/[Yb(dbm)₃L_S]·[Yb(dbm)₃(C₂H₅OH)] (D-2/L-2) were isolated, where btfa⁻ = 3-benzoyl-1,1,1-trifluoroacetonate, dbm⁻ = dibenzoylmethanate, and L_R/L_S = (−)/(+)-4,5-pinenepyridyl-2-pyrazine. D-1/L-1 possess mononuclear structures in which the Yb^III ions are eight-coordinated, while D-2/L-2 show cocrystal structures containing Yb(dbm)₃(L_R/L_S) and Yb(dbm)₃(C₂H₅OH) moieties in which the two Yb^III ions are eight and seven-coordinated, respectively. They not only feature different molecular structures but also present distinct linear and nonlinear optical performances. Chiral mononuclear D-1 has better near infrared photo-luminescence (NIR-PL) and circularly polarized luminescence (CPL) performances than chiral cocrystal D-2. More remarkably, D-1/L-1 show large second-harmonic generation (SHG) responses (up to 1.25/1.28 × KDP) 18/16 times those of D-2/L-2 (0.07/0.08 × KDP). In addition, D-2/L-2 represent the first examples of lanthanide cocrystal complexes with NIR-PL, NIR-CPL and SHG properties.