title: Electroactive thiazole derivatives capped with ferrocenyl units showing charge-transfer transition and selective ion-sensing properties: a combined experimental and theoretical study.
abstract: The synthesis, optical and electrochemical properties, and X-ray characterization of two thiazole derivatives capped by ferrocenyl groups (5 and 7) and their model compounds with one ferrocenyl, either at 2 or 5 position of the mono- or bis-thiazolyl rings (3, 9, 11, and 14), are presented. Bisferrocenyl thiazole 5 forms the mixed-valence species 5*+ by partial oxidation which, interestingly, shows an intramolecular electron-transfer phenomenon. Moreover, the reported heteroaromatic compounds show selective ion-sensing properties. Thus, ferrocenylthiazoles linked across the 5 position of the heteroaromatic ring are selective chemosensors for Hg2+ and Pb2+ metal ions; 5-ferrocenylthiazole 3 operates through two channels, optical and redox, for Hg2+ and only optical for Pb2+, whereas 1,1'-bis(thiazolyl)ferrocene 14 is only an optical sensor for both metal ions. Moreover, complex 3 behaves as an electrochemically induced switchable chemosensor because of the low metal-ion affinity of the oxidized 3*+ species. On the other hand, ferrocenylthiazole 9, in which the heterocyclic ring and the ferrocene group are linked across the 2 position, is a selective redox sensor for Hg2+ metal ions, and it responds optically, as does bis(thiazolyl)ferrocene 11, to a narrow range of cations (Zn2+, Cd2+, Hg2+, Ni2+, and Pb2+). Finally, bis(ferrocenyl)thiazole 5 is a dual optical and redox sensor for Zn2+, Cd2+, Hg2+, Ni2+, and Pb2+, whereas bis(ferrocenyl) compound 7, bearing a bis(thiazole) unit as a bridge, is only a chromogenic sensor for Zn2+, Cd2+, Hg2+, Ni2+, and Pb2+. The experimental data and conclusions about both the electronic and ion-sensing properties are supported by DFT calculations which show, in addition, an unprecedented intramolecular electron-transfer reorganization after the first one-electron oxidation of compound 5.
authors.affiliation: Departamento de Química OrgAnica, Facultad de Química, Campus de Espinardo, Universidad de Murcia, E-30100 Murcia, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Caballero
authors.forename: Vega
authors.initials: V
authors.lastname: Lloveras
authors.forename: David
authors.initials: D
authors.lastname: Curiel
authors.forename: Alberto
authors.initials: A
authors.lastname: Tárraga
authors.forename: Arturo
authors.initials: A
authors.lastname: Espinosa
authors.forename: Rafaela
authors.initials: R
authors.lastname: García
authors.forename: José
authors.initials: J
authors.lastname: Vidal-Gancedo
authors.forename: Concepció
authors.initials: C
authors.lastname: Rovira
authors.forename: Klaus
authors.initials: K
authors.lastname: Wurst
authors.forename: Pedro
authors.initials: P
authors.lastname: Molina
authors.forename: Jaume
authors.initials: J
authors.lastname: Veciana