Synthesis of NIR‐II Fluorophores by a C(sp2)‒C(sp2/sp) Coupling Reaction Driven by Charge‐Transfer Interaction

Here, we report a C(sp2)‒C(sp2/sp) coupling reaction driven by charge transfer interaction. Due to the strong intermolecular noncovalent interaction, an essential electron donor‐acceptor (EDA) complex is formed, confirmed solidly by absorption spectra, 1H NMR and single crystal X‐ray diffraction. The EDA complex lowers the activation barrier (Ea = 9.17 kcal/mol) and facilitates the formation of the C‒C bond, which is the rate‐limiting step revealed by H/D and 12C/13C KIE studies. Kinetic investigations reveal that the reaction is a second‐order reaction. Furthermore, high‐level theoretical calculations support the proposed mechanism. The mono‐ and di‐substituted products were obtained by varying the reaction conditions. A series of structurally diverse and novel NIR‐II fluorophores based on benzo[1,2‐c:4,5‐c’]bis([1,2,5]thiadiazole) (BBTD) were synthesized by utilizing this coupling reaction.