title: Upper rim allyl- and arylazo-coupled calix[4]arenes as highly sensitive chromogenic sensors for Hg2+ ion.
abstract: The syntheses and chromogenic properties of calix[4]arenes, carrying 5,17-bisallyl-11,23-bis(p-X-phenyl)azo 3a-c, 5,11,17-triallyl-23-(p-X-phenyl)azo 4a-c, and 5,17-bis(hydroxypropyl)-11,23-bis(p-X-phenyl)azo groups on the upper rims 5a,b, are described. Unexpectedly, UV/vis spectra of the very popular 4-(4-nitrophenyl)azophenol-coupled calix[4]arenes 3c and 4c did not show any shift in lambda(max) when 10 different metal perchlorates were added separately to the host in a methanol-chloroform (v/v = 1/399) cosolvent. In contrast, the absorption spectra of calix[4]arenes with either 4-methoxyphenylazo (3b-5b) or 4-phenylazo (3a-5a) on the upper rim showed substantial bathochromic shifts (Deltalambda = 128-162 nm) upon the addition of soft metal ions (such as Hg(2+), Cr(3+), and Cu(2+)). The 4-(4-methoxyphenyl)azophenol-coupled calix[4]arenes (the 3b-5b series) are found to be highly sensitive for mercury ion (Hg(2+)) among the 10 different metal ions screened. Strong interactions between Hg(2+) ion and the 4-(4-methoxyphenyl)azophenol(s) as well as the p-allyl groups are corroborated by the (1)H NMR studies of 3a,b.Hg(2+) complexes. Furthermore, Job's plots revealed 1:1 binding stoichiometry for all these p-allyl- and arylazo-coupled calix[4]arenes with transition metal ions, and Benesi-Hilderbrand plots were used for the determination of their association constants.
authors.affiliation: Department of Applied Chemistry, Center for Interdisciplinary Molecular Science, National Chiao Tung University, Hsinchu, Taiwan 30050, R.O.C.
authors.forename: Tsui-Lien
authors.initials: TL
authors.lastname: Kao
authors.forename: Chiung-Chiu
authors.initials: CC
authors.lastname: Wang
authors.forename: Yu-Ting
authors.initials: YT
authors.lastname: Pan
authors.forename: Ya-Jiun
authors.initials: YJ
authors.lastname: Shiao
authors.forename: Jhy-Yuan
authors.initials: JY
authors.lastname: Yen
authors.forename: Chun-Mei
authors.initials: CM
authors.lastname: Shu
authors.forename: Gene-Hsiang
authors.initials: GH
authors.lastname: Lee
authors.forename: Shie-Ming
authors.initials: SM
authors.lastname: Peng
authors.forename: Wen-Sheng
authors.initials: WS
authors.lastname: Chung