Donor-Acceptor Architecture Dictates Emission Properties: Enhanced Solid-State Fluorescence in Carbazole-Based Charge Transfer Cocrystals

Abstract

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 molecules (9-phenyl-9H-carbazole (PC), and 9-(p-tolyl)-9H-carbazole (TC)) and acceptor 2,3,5,6-tetrafluoroterephthalonitrile (TFN), 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.