Modulating Linker Conjugation and Flexibility of Aggregation‐Induced Emission Covalent Organic Framework for Enhanced Luminescence

Abstract In order to inhibit non‐radiative decay pathways of covalent‐organic frameworks (COFs), a strategy is proposed to block intralayer conjugation and interlayer π–π stacking by using flexible aggregation‐induced emission (AIE) building blocks (4′,4′′′,4′′′′′,4′′′′′′′‐(1,2‐ethenediylidene) tetrakis[1,1′‐biphenyl]‐4‐carbaldehyde (TFBE)) connected by weakly conjugated flexible linker. By using the flexible TFBE as building blocks and changing the conjugation and flexibility of linker, TFBE‐COFs with different luminescence properties are obtained. Experimental and theoretical results show that these TFBE‐COFs have high crystallinity and large layer spacing, among which the photoluminescence quantum yield of hydrazone (Hz)‐COF TFBE‐ODH (oxalyl dihydrazide (ODH)) in solid state reaches 26.28%, which is superior to most of the COFs reported so far. The excellent luminescence is attributed to the non‐planar geometry and flexibility of TFBE, which inhibits aggregation‐induced quenching. Moreover, the π‐electron delocalization‐induced non‐radiative leaps are suppressed by weakly conjugated flexible linker, which further enhances the photoluminescence of TFBE‐COFs. The Hz‐COF TFBE‐ODH exhibits excellent sensing performance for trace tetracycline, the detection limit is 0.15 µ m . In addition, a white light‐emitting diodes coated with Hz‐COF TFBE‐ODH is manufactured to achieve high‐quality white light emission. This study provides a new strategy for the design and application of high‐emission COFs.