Absorption, fluorescence, and cd spectroscopic study of chiral recognition by a binaphthyl‐derived chromogenic calixcrown host

The (R)‐ and (S)‐enantiomers of a binaphthyl‐appended calix4crown‐6 ether with two 2,4‐dinitrophenylazo chromophore units ((R)‐ 1 and (S)‐ 1 ) as chiral hosts were tested in their reactions with the enantiomers of α‐methylbenzylamine ((R)‐MBA, (S)‐MBA)) and phenylglycinol ((R)‐PGL, (S)‐PGL) as chiral guests. The visible absorption spectra indicate a two‐step process: the first is a nonenantioselective proton transfer from the host to the guest, which is followed by the enantioselective real complexation. In the visible range of the CD spectra a positive/negative band belongs to the absorption of pure (R)‐ 1 /(S)‐ 1 , and a negative/positive exciton couplet to the absorption of (R)‐ 1 ‐(S)‐MBA/(S)‐ 1 ‐(R)‐MBA complexes. The latter phenomenon suggests that the complexation of amines is accompanied by a chiral arrangement of the two chromophore units in the hosts. The UV fluorescence of (R)‐ 1 /(S)‐ 1 arising from the binaphthyl moiety is quenched by K + ions, but not by the amine guests, showing that the interaction between the binaphthyl group and the complexed amines is weak. Chirality 16:174–179, 2004 . © 2004 Wiley‐Liss, Inc.