Donor conjugation engineered heteroligand metal organic frameworks with a near-dark state for multicolor fluorescence-responsive sensing.

Multicolor fluorescence-responsive metal-organic frameworks (MOFs) have drawn considerable attention for advanced smart sensing. Using aggregation-induced emission donor together with aggregate-caused quenching acceptor offers a viable solution for constructing MOFs with near-dark states that are favorable for high signal-to-noise ratio turn-on sensing. Conventional strategies commonly rely on the luminescent unit screening to regulate the optical properties between the donor and acceptor of MOFs. However, identifying donor and acceptor pairs with well-matched optical properties and suitable energy levels to facilitate electron transfer remains challenging. Herein, we propose a donor conjugation engineering strategy to systematically regulate interligand motion/stacking and electron transfer by tuning the conjugation degree of the donor. Three heteroligand MOFs containing a common meso-tetra(4-carboxyphenyl)porphine acceptor, and different tetraphenylethylene-based donors with different numbers of conjugated benzene rings were examined. The resulting materials exhibited a progression from a dark state, to a near-dark state, and then to weak emission as donor conjugation increased. Among them, Zr-ETTC-TC with near-dark state is activated under extremely weak stimuli, demonstrating the highest sensitivity and concentration-dependent multicolor response toward multiple targets (sulfide and ammonia), ranging from near-dark to red, orange, yellow, and green, supporting its potential in the detection of sulfide in water and real-time monitoring of food spoilage.