Donor–acceptor architecture dictates emission properties: enhanced solid-state fluorescence in carbazole-based charge transfer cocrystals

The ability to precisely control fluorescence variations holds significant promise for applications in advanced display technologies, bioimaging, and optical sensors. However, achieving solid-state emission enhancement within a single system remains a challenge. In this study, we have developed two-component charge transfer (CT) aggregates composed of carbazole-derived donor (9-phenyl-9H-carbazole (PC) and 9-(p-tolyl)-9H-carbazole (TC)) and acceptor (2,3,5,6-tetrafluoroterephthalonitrile (TFN)) molecules exhibiting distinct enhancement in solid-state emission properties. Structural analysis reveals that the PC–TFN (4 : 1) cocrystal adopts a DAD⋯DAD configuration, while the TC–TFN (1 : 1) cocrystal forms a DADA arrangement, indicating strong CT interactions. The cocrystals exhibit a pronounced redshift in both UV absorption and fluorescence emission along with enhanced fluorescence quantum yields of 74.70% for PC–TFN and 54.07% for TC–TFN, and extended lifetime attributed to the CT interactions facilitated by π⋯π stacking between donor and acceptor molecules. Furthermore, quantum chemical calculations offer detailed insights into the modulation of luminescence properties, providing a more profound understanding of CT interactions and presenting a new strategy for designing materials with tunable fluorescence behavior.