Tuning oxygen-sensing behaviour of a porous coordination framework by a guest fluorophore

Abstract

Tris(8-hydroxyquinolinato)aluminium (AlQ₃), a classic fluorescent molecule insensitive to oxygen, is encapsulated as a guest fluorophore into a highly porous coordination framework [Zn₄O(bpz)₂(bdc)] (MAF-X10, H₂bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole, H₂bdc = 1,4-benzenedicarboxylic acid) to obtain a highly luminescent host–guest hybrid material AlQ₃@MAF-X10 combining the advantages of excellent fluorescence of AlQ₃, high oxygen permeability of MAF-X10, and the resonance energy transfer between AlQ₃ and MAF-X10. Photoluminescence studies showed that AlQ₃@MAF-X10 exhibits yellowish green fluorescence with a Stokes shift (9606 cm⁻¹) as large as those of phosphorescent noble metal complexes, long lifetime (37.4 ns) and a considerable oxygen permeability (4.4 × 10⁻⁹ mol cm⁻¹ s⁻¹ bar⁻¹), giving rise to high oxygen sensitivity (88.5% quenched at 1 bar, i.e., I₀/I₁₀₀ = 8.7, K_SV = 7.6 bar⁻¹) with fast response and good reversibility.