Abstract
This work deals with the development of water-soluble optical sensors based on ruthenium(II) tris(diimine) complexes that exhibit high molar absorptivity and are emissive in aqueous media. Palladium-catalyzed arylation of polyamines with 3-bromo-1,10-phenanthroline (Brphen) and [Ru(bpy)2(Brphen)](PF6)2 (bpy = 2,2’-bipyridine) was explored to prepare Ru2+ complexes with 1,10-phenanthrolines (phen) substituted by linear polyamines (PAs) at position 3 of the heterocycle ([Ru(bpy)2(phen–PA)](PF6)2). The most convenient synthetic pathway leading to the target molecular probes includes the preparation of phen–PA ligands, followed by ruthenium complexation using cis-Ru(bpy)2Cl2. Complexes bearing a polyamine chain directly linked to phenanthroline core are emissive in aqueous media and their quantum yields are comparable to that of parent [Ru(bpy)3](PF6)2. Their structure can be easily adapted for detection of various analytes by modification of amine groups. As an example, we prepared the emissive complex Ru(N2P2phen) which is suitable for the dual channel (spectrophotometry and luminescence (ON–OFF probe)) selective detection of Cu2+ ions at the physiological pH levels with limits of detection (LOD) by spectrophotometry and fluorescence spectroscopy equal to 9 and 6 μM, respectively, that is lower than the action level in drinking water for copper as prescribed by the US Environmental Protection Agency.
Highlights
Publisher’s Note: MDPI stays neutralThe design and synthesis of abiotic molecular systems capable of signaling various guest molecules or ions by changing optical properties has spurred tremendous research efforts [1]
We report on the synthesis of chemosensors bearing mixed ligand
Pd(dba)2 was synthesized according to a known method [26] and used without recrystallization. 3-Bromo-1,10-phenanthroline (2)
Summary
The design and synthesis of abiotic molecular systems capable of signaling various guest molecules or ions by changing optical properties has spurred tremendous research efforts [1]. Tris(diimine) complexes with aminophenanthroline ligands are strongly dependent on the position of the amino-substituent attached to the heterocycle, and emission quantum yields of complexes involving 4-substituted phen ligands are expected to be low [23,24] This could be detrimental for the sensibility of chemosensors. The introduction of the amino substituents in the 3- or 5-position of the 1,10-phenanthroline ring results only in a small decrease in luminescence quantum yields compared to that of the parent complex [Ru(bpy) (phen)](PF6 ) , while the brightness of the complexes with the 3-substituted ligands is comparable to that of the parent complex In these Ru2+ complexes, the signaling and receptor units are directly connected, and HOMO is localized on the aminophenanthroline ligand [24]. It was demonstrated that despite a high brightness of both complexes, only Ru(N2 P2 phen) allows for dual channel optical detection of Cu2+ ions in aqueous media including tap water
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