Synthesis, characterization and spectroscopic studies of two new schiff-base bithienyl pendant-armed 15-crown-5 molecular probes

Abstract

a b s t r a c tTwo new ligands provided with a 15-crown-5 as a receptor unit and bithiophen unit as an emissive probe have been synthesized and characterized in order to evaluate the coordination capabilities and their sensor effect. Ligand L1 presents an aromatic crown ether moiety that is directly linked to the imine-2,2 0 -bithiophene p-conjugated system, and ligand L2 is constituted by an aliphatic crown ether moiety that is linked to the same imine-2,2 0 -bithiophene system through a methylene unit. Solid metal complexes of Ni(II), Pd(II), Hg(II) and Na(I) have been synthesized using both macrocyclic compounds, and have been studied in solution in the presence of the same metal ions. All solid compounds have been characterized by common analytical and spectroscopic techniques. The sensorial effect has been studied using absorption, emission and MALDI-TOF-MS spectroscopies.Ó 2008 Elsevier B.V. All rights reserved.Very recently Gokel and coworkers [1] and Fery-Forgues and coworker [2] have reviewed the importance of the crown ethers as molecular sensors for ions, as molecular scaffolds and as complexing agents. Many of these systems are provided with rigid binding units, molecular tweezers, butterfly structures, molecular rods, etc., presenting two well defined coordination units.These compounds are very appealing due to their potential applications for simultaneous recognition of a transition metal ion and an alkaline or alkaline-earth metal ion [3][4][5][6]. The interaction with two metal ions normally modulates several interesting properties, as it has been reported previously. For example in compound I [3] (Scheme 1), the complexation capability was modulated by the alkaline Na(I), in compounds II and III, the redox behavior of the Ni(II) and Re(I) complexes, respectively, was modulated by the alkaline and alkaline earth metals [4,5]. Finally, the liquid crystal property in compound III has also been modulated in the presence of Na(I) [6]. Recently, we have synthesized and characterized several heterocyclic compounds functionalized with (oligo)thiophene p-conjugated systems for sensor applications [7]. Tertiary amines functionalized with a methylene crown ether moiety and two (oligo)thiophene pendants are one of the most recent examples of new heterocyclic sensors reported by us. In this case, Na(I) or H + modulated the intensity of the emission shown by the Pd(II) complexes [7d].Active molecules that interact with analytes through the enhancement of any particular property are very appellative for analytical applications; particularly active molecules to be detected and used by spectrometry techniques are very interesting for their further use as MS-active matrices [8].As a part of our research project in multifunctional/multisensorial molecular probes and keeping these alkaline/alkaline-earth modulation properties idea in mind, we report here two new compounds, L1 and L2 (Scheme 2), that are provided with a bithiophene emissive unit covalently linked through an imine bond to a 15-crown-5 chelating unit (...

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MALDI‐TOFMS analysis of coordination and organometallic complexes: a nic(h)e area to work in

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