Imidazole/benzimidazole-modified cyclotriphosphazenes as highly selective fluorescent probes for Cu: synthesis, configurational isomers, and crystal structures

• Published in: Dalton transactions : an international journal of inorganic chemistry 2017-07, Vol.46 (28), p.914-9156
• Main Authors: Uslu, Aylin, Tümay, Süreyya O uz, enocak, Ahmet, Yuksel, Fatma, Özcan, Elif, Ye ilot, Serkan
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c7dt01134b

Configurational isomers ( cis and trans ) of imidazole- or benzimidazole-modified cyclotriphosphazenes ( 3a , 4a or 3b , 4b ) were designed, synthesized and investigated as fluorescent probes for metal ions. The newly synthesized compounds were characterized by 1 H and 31 P NMR, and MALDI MS spectrometry. The configurations of geometric isomers were analyzed by X-ray crystallography and 31 P NMR spectroscopy on addition of CSA. The photophysical behaviour and metal ion selectivity of the compounds were investigated by UV/vis and fluorescence spectroscopy. Among the examined 20 metal ions, the fluorescence emissions of the isomer mixtures were quenched by Cu 2+ together with Fe 2+ , Fe 3+ , Zn 2+ and Ni 2+ ions, but each individual isomer ( 3a,b and 4a,b ) exhibited an on-off-type fluorescence response with high selectivity towards only Cu 2+ with a low limit of detection ranging from 1.27 μM to 2.04 μM. The complex stoichiometries of 3a,b and 4a,b with Cu 2+ were determined as 1 : 1 (L/M) using the method of continuous variation (Job's plot) and density functional theory (DFT) calculations; moreover the complex formation of 4a with Cu 2+ was unambiguously determined by X-ray crystallographic analysis that is consistent with the results obtained by the Job's plots as well as DFT. We present a comprehensive work and discuss the fluoroprobe properties of synthesized compounds for copper ion detection with a stereochemical approach using X-ray crystallographic analysis results.