A Highly Fluorescent Metallosalalen-Based Chiral Cage for Enantioselective Recognition and Sensing

• Published in: Chemistry : a European journal 2014-05, Vol.20 (21), p.6455-6461
• Main Authors: Dong, Jinqiao, Zhou, Yanfang, Zhang, Fangwei, Cui, Yong
• Format: Article
• Language: English
• Subjects: Amines; Cage; Cage molecules; Carbohydrates; Chemistry; chirality; Circular dichroism; coordination cage; Detection; Dichroism; Enantiomers; Fluorescence; fluorescence sensor; Holes; Iodides; metal-organic frameworks; metallosalalen; Networks; Rigidity; Saccharides; Spectroscopy; Thermogravimetric analysis; Three dimensional; X-rays
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201304606

A highly fluorescent coordination cage [Zn8L4I8] has been constructed by treating enantiopure pyridyl‐functionalized metallosalalen units (L) with zinc(II) iodide and characterized by a variety of techniques including microanalysis, thermogravimetric analysis (TGA), circular dichroism (CD) spectroscopy, and single‐crystal and powder X‐ray diffraction. Strong intermolecular π–π, CH⋅⋅⋅π, and CH⋅⋅⋅I interactions direct packing of the cage molecules to generate a 3D polycage network interconnected by pentahedral cages formed by adjacent pentamers. The cage has an amphiphilic helical cavity decorated with chiral NH functionalities capable of interactions with guest species such as saccharides. The fluorescence of the cage was greatly enhanced by five enantiomeric saccharides in solution, with enantioselectivity factors of 2.480–4.943, and by five enantiomeric amines in the solid state, with enantioselective fluorescence enhancement ratios of 1.30–3.60. This remarkable chiral sensing of both saccharides and amines with impressive enantioselectivity may result from the steric confinement of the cavity as well as its conformational rigidity. It holds great promise for the development of novel chiral cage materials for sensing applications. Cage‐based chiral sensor: A highly fluorescent coordination cage [Zn8L4I8] can be prepared from enantiopure pyridyl‐functionalized metallosalalen units (L). The cage has an amphiphilic helical cavity decorated with chiral NH functionalities and supramolecular interactions generate a 3D polycage network interconnected by pentahedral cages formed by adjacent pentamers (see graphic). The fluorescence of the cage is greatly enhanced either in solution or in the solid state in the presence of enantiomeric saccharides or amines, respectively, with significant enantioselectivity factors.