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[Display omitted] • Flexible ligand strategy was first proposed to prepare MOFs with simultaneous large-pore and antenna effect emission. • Flexible –CH 2 -O- group can tune the energy level of ligand. • Different diffusion dynamics was observed for MOFs with different pore sizes. • The relative specific surface area affected the linear response range. • L1-Eu MOF sensor realized the ratiometric fluorescence detection of PO 4 3- and ATP. Polycyclic aromatic ligands improve the pore size of metal–organic frameworks (MOFs), but their big π-conjugation structure forbids energy transfer for antenna effect emission. Thus, large-pore and antenna effect are a dilemma even their combination could improve the efficiency of MOFs. Herein, we construct a flexible ligand, 1,3,5-tris(5-methoxy-1,3-benzene dicarboxylic acid)benzene (L1) by attaching three isophthalic acids (L2) to a benzene ring through flexible –CH 2 -O- bonds. L1 retains the optical properties of L2 for antenna effect and expands the molecular size for MOFs with large pore. Single-crystal result of the MOFs obtained with L1 and Eu3+, Tb3+, or Gd3+ reveals the aperture of 18 Å and the density of 1.2 g/mL. L1 excites Eu3+ and Tb3+ ions for their antenna effect emission. The –CH 2 -O- group tunes the energy transfer for dual-emission at 360 and 623 nm from L1 -Eu MOF under single excitation of 290 nm. The dual-emission is used for ratiometric fluorescence detection of phosphate (PO 4 3-) and adenosine-5′-triphosphate (ATP). We reveal the effect of porous structure of MOFs on the response speed and range. The pore size affects the target entrance as L1 -Eu MOF shows faster response to PO 4 3- and ATP than L2 -Eu MOF. Moreover, fast diffusion dynamics of a target is observed in large-pore MOFs for good linear response. The relative specific surface area affects the linear range as a narrower range was observed for ATP than PO 4 3-. Thus, flexible ligand is effective to expand the aperture, improve optical properties, and study the response mechanism for the extensive applications of MOFs. [ABSTRACT FROM AUTHOR]