Reversible trans -to- cis photoisomerization and irreversible photocyclization reactions of a Co-coordinated stilbene derivative on chiral di-β-diketonate lanthanide complexes.

Six lanthanide complexes constructed from two chiral β-diketonates (d/l-fbc = 3-heptafluorobutyry l- (+)/(-)-camphorate), the stilbene derivative ( E )- N ', N '-bis(pyridin-2-ylmethyl)-4-styrylbenzoyl hydrazide (L), a trifluoroacetate anion (CF 3 CO 2 - ), and one water molecule, namely [Ln(d/l-fbc) 2 (L)(CF 3 CO 2 )]·H 2 O (LnC 57 H 54 F 17 N 4 O 8 , Ln = La (1, d-fbc), La (2, l - fbc), Sm (3, d-fbc), Eu (4, d-fbc), Eu (5, l - fbc), and Tb (6, d-fbc), were synthesized and characterized by single-crystal X-ray diffraction, 1 H-NMR, elemental analysis, IR and UV-vis spectroscopy, and thermal gravimetric analysis. The photoisomerization reactions of these complexes were systematically studied by means of experimental and theoretical calculations. Crystals of complexes 1, 2, 3, and 4 were obtained and belong to the monoclinic crystal system and the C 2 chiral space group. The Λ- and Δ-diastereomers coexist in their crystals and no apparent bisignate couplets are observed in their ECD spectra. Among the complexes, the photocyclization reaction is followed by the trans -to- cis photoisomerization reaction and competes with the trans -to- cis photoisomerization, then the photocyclization reaction continues. The photocyclization reaction is irreversible in this stilbene derivative and is delayed in the lanthanide complexes. These results provide a viable strategy for the design of promising new stilbene-attached dual-functional lanthanide-based optical-switching materials.