Furan‐modified thiadiazolo quinoxaline as an electron acceptor for constructing second near‐infrared aggregation‐induced emission fluorophores for beyond 1300 nm fluorescence/photoacoustic imaging and photothermal therapy

Abstract Creation of new fluorophores is important for understanding the structure–property relationship, by which the required optical properties are likely to be attained. Herein, through theory calculation, it is found that furan‐modified thiadiazolo quinoxaline acting as an electron acceptor can endow donor–acceptor–donor (D–A–D) type second near‐infrared (NIR‐II) fluorophores with longer emission wavelength than the other thiadiazolo quinoxaline‐based acceptors containing pyridine, pyrrole, thiophene, and phenyl groups, respectively. On the basis of this theoretical prediction, a D–A–D type NIR‐II fluorophore with 6,7‐di(furan‐2‐yl)‐[1,2,5]thiadiazolo[3,4‐g] quinoxaline (DFTQ) as the acceptor and dithieno[3,2‐b:2′,3′‐d]pyrrole (DTP) as the donor is designed and synthesized, and the aggregation‐induced emission (AIE) function is further achieved by introducing the AIE units of tetraphenylethylene (TPE) and triphenylamine (TPA), respectively, totally forming three NIR‐II fluorophores DFTQ–DTP, DFTQ–DTPE, and DFTQ–DTPA. For biological applications, the fluorophores are encapsulated by amphiphilic DSPE–PEG 2000 to generate water‐dispersible nanoparticles (NPs). Almost the whole emission of each of the NPs falls into the NIR‐II spectral range, with part emission beyond 1300 nm. By using DFTQ–DTPA NPs as the contrast and photothermal therapy (PTT) agent, high‐resolution in vivo fluorescence imaging is achieved in the greater than 1300 nm window, and their good performance in photoacoustic imaging and high tumor PTT efficacy in tumor‐bearing mice are also demonstrated. Taken together, this work mainly provides a strong electron acceptor for constructing long‐emitting fluorophores, and by using the electron acceptor, a AIE fluorophore with desirable quantum yield (QY) and photothermal conversion efficienciy (PCE) is synthesized and demonstrated to be promising in fluorescence/photoacoustic imaging and PTT.