To overcome the non-radiative energy dissipation that weakens the intrinsic emission of metal-organic frameworks (MOFs), a fluorophore functionalization strategy was applied to restrict intramolecular ligand motion and to enhance the photoluminescence. Two analogous frameworks were synthesized and systematically compared: {[Cd(4bpyttz)(CDA)]·2DMF}_n (MOF 1), constructed from a ligand with a rigidly fused thiazolo[5,4-d]thiazole (TTZ) core, and [Cd(4bbpy)(CDA)]_n (MOF 2), which incorporates a freely rotatable phenyl core (4bpyttz=2,5-bis(pyridin-4-yl)thiazolo[5,4-d]thiazole, 4bbpy=1,4-bis(pyridin-4-yl)benzene, H₂CDA=4,4′-carbonyldibenzoic acid). Photophysical and density functional theory (DFT) studies reveal that the TTZ core localizes both the HOMO and LUMO on itself, thereby deactivating the ligand-to-ligand charge transfer (LLCT) pathway present in MOF 1. This core rigidification enforces ordered π…π stacking and suppresses non-radiative decay, leading to dramatically enhanced solid-state photoluminescence. Consequently, MOF 1 functions as a highly selective turn-off fluorescent sensor for nitrofuran antibiotics in aqueous media, achieving limits of detection of 1.59 μmol·L^-1 for nitrofurazone (NZF) and 2.77 μmol·L^-1 for nitrofurantoin (NFT). Mechanistic studies show that this rapid quenching is primarily governed by the inner filter effect (IFE) coupled with photoinduced electron transfer (PET).