Well-defined enantiopure 1,1'-binaphthyl-based oligomers: synthesis,structure, photophysical properties,and chiral sensing

A series of well-defined enantiopure 1,1'-binaphthyl-based oligomers linked through their 6,6'-positions, ranging from quaternaphthol to decanaphthol, have been synthesized by Suzuki and Stille coupling reactions. These novel oligonaphthyls have been characterized by (1)H and (13)C[(1)H] NMR spectroscopy and high-resolution mass spectrometry. A combination of X-ray structural and CD studies suggests that these oligonaphthyls adopt zigzag but not helical conformations. As the chain length increases, the compounds show enhanced fluorescence. The fluorescence intensity of oligonaphthols is almost 2 orders of magnitude higher than that of 1,1'-bi-2-naphthol and can be effectively and enantioselectively quenched with trans-1,2-diaminocyclohexane with an enantioselectivity factor of 1.24. The present work thus demonstrates the potential of constructing chiral sensory materials based on well-defined enantiopure oligonaphthols.