Acceptor-Induced Cooperative Mixed-Stacking Supramolecular Co-Assembly with Enhanced Emissive Characteristics

Charge transfer (CT) cocrystals provide a means to modify the photophysical features of organic-based fluorophores in the aggregate state. In cocrystals, the degree of CT depends not only on the donor (D) and acceptor (A) characteristics of the constituents but also on their molecular packing. In this study, two novel mixed stacked cocrystals (DA1 and DA2) based on DITFB (diiodo-tetrafluorobenzene) and TCNB (1,2,4,5-tetracyanobenzene) as acceptor units with 3-(6-methoxynaphthalen-2-yl)-2-(pyridin-4-yl) acrylonitrile (D) serving as an electron donor were achieved via halogen/hydrogen bonding and CT interactions (CTI). Due to the enhanced CTI, these two cocrystals display red-shifted emissions from 508 to 572 nm in the condensed state. Single-crystal investigation indicates that the distance between D and A in supramolecular assembly influences the CT degree; a fully face-to-face stacking between D and A considerably increases the CT degree. More significantly, the acceptors play a foremost role in regulating the fluorescence features of cocrystals. DFT calculations were utilized to get insight into the CTI and between D and A, indicating that the CTI significantly impacts the energy levels and orbital distributions. We believe that this strategy can lead to the development of more efficient CT cocrystals with outstanding emissive properties.