The nature of 6,6′-bis(triphenylamine) substituted BINOL as chromophoric and fluorogenic hybrid chemosensor for selective fluoride detection

Abstract

6,6′-Bis(triphenylamine)-1,1′-binaphthyl-2,2′-diol ( 1) is highly fluorescent in visible region. On treatment with a variety of anions, the UV–vis absorption as well as the fluorescent behavior of 1 in CH 2Cl 2 is substantially changed. Among the tetrabutylammonium (TBA) salts we tested, including F −, OH − (from TBAOH in MeOH), Cl −, Br −, I −, OAc −, HSO 4 −, TsO − (Et 4N salt), and H 2PO 4 −, F − was found to be the most effective fluorescence quencher. Quantitative fluorescence analysis of the titration data revealed that the anions are classified into two categories: (1) Simple mono-anions, such as F − ( log β 2 F = 11.00 ± 0.08 ) , OH − ( log β 2 OH = 9.05 ± 0.01 ) , and Cl − ( log β 2 = 9.96 ± 0.70 ) that follow the stoichiometry of 1:2, indicating the formation of ( 1·X 2) 2− complexes; (2) Oxo-anions, such as OAc − ( log β 1 OAc = 5.13 ± 0.012 ) , H 2PO − 4 ( log β 1 HP = 4.87 ± 0.03 ) , and TsO − (using tetraethylammonium salt, ( log β 1 OTs = 3.36 ± 0.02 ) that show the stoichiometry of 1:1, indicating the formation of ( 1·X) − complexes. The complexation behaviors were further confirmed by 1H NMR spectroscopy. In the co-crystal prepared from 1,1-binaphthyl-2,2′-diol (BINOL) and Et 4NF, F − and BINOL are assembled to form a linear polymeric array, with a dimeric group of BINOL/BINOL anions linked as the side-chains. Intramolecular hydrogen bond was observed within the BINOL anion. This provides structural insights about the BINOL–fluoride complex formation.