Chiral and non-conjugated fluorescent salen ligands:AIE, anion probes, chiral recognition of unprotected amino acids, and cellimaging applications

G. Y. Shen, F. Gou, J. H. Cheng, X. H. Zhang, X. G.Zhou, and H. F. Xiang,*, RSC Adv., 2017, 7, 40640-40649.

Natural products are usually non-conjugated and chiral, but organic luminescent materials are commonlypolycyclic aromatic molecules with extended $\pi$ -conjugation. In the present work, we combine with theadvantages of non-conjugation and chirality to prepare a series of novel and simple salen ligands(41 samples), which have a non-conjugated and chiral (S,S) and (R,R) cyclohexane or 1,2-diphenylethanebridge but display strong blue, green, and red aggregation-induced emission (AIE) with large Stokes shifts(up to 186 nm) and high fluorescence quantum yields (up to 0.35). Through hydrogen and halogenbonds, these flexible salen ligands can be used as universal anion probes and chiral receptors ofunprotected amino acids (enantiomeric selectivity up to 0.11) with fluorescence quantum yields up to0.29 and 0.27, respectively. Moreover, the effects of different chiral bridges on the moleculearrangement, AIE, and anion and chiral recognition properties are also explored, which provideunequivocal insights for the design of non-conjugated chiral and soft fluorescent materials.