Turn-on fluorescent probe towards glyphosate and Cr3+ based on Cd(ii)-metal organic framework with Lewis basic sites

A microcrystalline Cd(ii)-MOF, [Cd(NH2-bdc)(azp)]center dot DMF (NH2-H(2)bdc = 2-amino-1,4-benzenedicarboxylic acid and azp = 4,4 '-azopyridine), namely 1-NH2 was rationally designed and synthesized as a fluorescent sensor in the off state utilizing the photo-induced electron transfer (PET) process. The crystal structure of 1-NH2 features a porous 2-fold interpenetrated 3D framework with 1D channels decorated with open Lewis basic amino and azo groups for recognizing the target species. Time-dependent density functional theory (TD-DFT) calculations were performed to gain insight into the PET process that induces the fluorescent quenching of 1-NH2. The proposed 1-NH2 is the first MOF that presents highly selective and sensitive visual turn-on fluorescence detection of glyphosate and Cr3+ with very low detection limits of 25 nM and 0.6 mu M, respectively. The amino moiety in 1-NH2 plays a key role for the selective binding of Cr3+ to facilitate the sensitivity and selectivity of the detection. The fluorescent enhancement mechanism is associated with the inhibition of the PET process stimulated by the dissociation of the framework of 1-NH2 in the presence of glyphosate and Cr3+.

Automated summary

A newly designed microcrystalline Cd(ii)-MOF fluorescent sensor, 1-NH2, was synthesized for off-state detection utilizing the photo-induced electron transfer process, showing high selectivity and sensitivity, especially towards glyphosate and Cr3+ with low detection limits. The fluororescent enhancement mechanism is associated with the inhibition of the PET process stimulated by the dissociation of the framework in the presence of glyphosate and Cr3+.