A facile “dots-in-zeolites” strategy is developed to synthesize a new class of CD-based TADF materials with ultralong lifetimes.

Confining carbon dots (CDs) in zeolites may boost the thermally activated delayed fluorescence (TADF) emission. However, so far only blue-emissive CD-based TADF materials are reported, and rationally tuning the TADF emission of these materials remains challenging. Herein, by in situ embedding different emissive CDs into a zeolite matrix, we have successfully prepared a series of CD@zeolite composites with tunable TADF emission from blue to green by utilizing energy transfer (ET) between confined CDs. The as-prepared CD@zeolite composites exhibit lifetimes varying from 271 ms to 860 ms and quantum yields ranging from 20% to 42%. The ET process occurs from the singlet excited state of the blue emissive CD donor to the singlet excited state of green emissive CD acceptors with different polymerization degrees, promoting tunable TADF with cyan, mint green and olive green emission. The design concept proposed in this work may open a way to judicious tuning of the emission of TADF materials, and thus may broaden the applications of CD-based TADF materials.