Stable terbium metal–organic framework with turn-on and blue-shift fluorescence sensing for acidic amino acids (l-aspartate and l-glutamine) and cations (Al3+ and Ga3+)

Abstract

A terbium-based metal–organic framework, namely {[Tb₂(ADIP)(H₂ADIP)(HCOOH)(H₂O)₂]·2DMF·2H₂O}_n (Tb-MOF, H₄ADIP = 5,5′-(anthracene-9,10-diyl) diisophthalic acid), was synthesized and characterized. The single-crystal structure analysis shows that the Tb-MOF crystallizes in the C₂/_C space group in the monoclinic system and its asymmetric unit contains two Tb^III ions, one ADIP⁴⁻, one H₂ADIP²⁻, one coordinating formic acid and two coordination water molecules. Tb-MOF has a three-dimensional porous structure with a porosity of 41.5%. Tb-MOF is a highly selective and sensitive fluorescence turn-on and blue-shift sensor for L-aspartate (Asp), L-glutamine (Glu), Al³⁺ and Ga³⁺with detection limits of 0.25, 0.23, 0.069 and 0.079 μM, respectively. Experimental studies and theoretical calculations show that the sensing process is mainly attributed to the energy transfer and the absorbance caused enhancement (ACE) mechanism. Therefore, Tb-MOF is a good multi-response fluorescence sensor for acidic amino acids and Al³⁺, Ga³⁺cations.