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Issue 20, 2020
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Robust fluorescent calcium coordination polymers as Cu2+ sensors with high sensitivity and fast response

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Abstract

A three-dimensional (3D) and highly fluorescent calcium-based coordination polymer (Ca-CP) has been synthesized and structurally characterized. Built on a strongly fluorescent (FL) chromophore ligand, [Ca(H2tcbpe)(H2O)2] (1) (H4tcbpe = 4′,4′′′,4′′′′′,4′′′′′′′-(ethene-1,1,2,2-tetrayl)tetrakis(([1,1′-biphenyl]-4-carboxylic acid))) is highly luminescent. Photoluminescence (PL) studies indicate that 1 undergoes a bathochromic shift in emission energy from blue to green color upon outgassing or under mechanic force. Notably, 1 exhibits selective FL sensing for Cu2+ ions with a detection limit (LOD) of 0.064 ppm, far below the U.S. WHO and EPA standard for drinking water. Detailed investigation of the sensing mechanism reveals that uncoordinated COO groups in 1 play a major role in recognizing Cu2+ ions. This is supported through analysis by multiple characterization methods including IR, EDS and XPS. Based on the proposed mechanism, an isostructural [Ca(H2tcbpe-F)(H2O)2] Ca-CP (2) (H4tcbpe-F = 4′,4′′′,4′′′′′,4′′′′′′′-(ethene-1,1,2,2-tetrayl)tetrakis(3-fluoro-[1,1′-biphenyl]-4-carboxylic acid)) is synthesized and tested. Compound 2 demonstrates a ten-fold enhancement in Cu2+ detection sensitivity with a ppb level detection limit. The strong enhancement in the detection sensitivity results from optimized electron density around free COO groups by introducing electron withdrawing F groups onto the backbone of the organic linker. Excellent chemical stability under a wide range of pH conditions (1–14), high sensitivity and rapid fluorescence quenching response time (seconds) make these compounds ideal candidates for use as Cu2+ sensors.

Graphical abstract: Robust fluorescent calcium coordination polymers as Cu2+ sensors with high sensitivity and fast response

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Supplementary files

Article information


Submitted
18 Feb 2020
Accepted
15 Apr 2020
First published
15 Apr 2020

J. Mater. Chem. C, 2020,8, 6820-6825
Article type
Paper

Robust fluorescent calcium coordination polymers as Cu2+ sensors with high sensitivity and fast response

Z. Wu, E. Velasco, C. Shan, K. Tan, Z. Zhang, Q. Hu, K. Xing, X. Huang and J. Li, J. Mater. Chem. C, 2020, 8, 6820
DOI: 10.1039/D0TC00825G

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