Synthesis of NIR‐II Fluorophores by a C(sp ² )−C(sp ² /sp) Coupling Reaction Driven by Charge‐Transfer Interaction

Abstract Here, we report a C(sp 2 )−C(sp 2 /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, 1 H NMR and single crystal X‐ray diffraction. The EDA complex lowers the activation barrier ( E a =9.17 kcal/mol) and facilitates the formation of the C−C bond, which is the rate‐limiting step revealed by H/D and 12 C/ 13 C 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 second near‐infrared (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.