Synthesis and Characterization of Novel Thienothiadiazole-Based D−π–A−π–D Fluorophores as Potential NIR Imaging Agents

As fluorescence bioimaging has increased in popularity, there have been numerous reports on designing organic fluorophores with desirable properties amenable to perform this task, specifically emission the near-infrared II (NIR-II) region. One such strategy is utilize donor−π–acceptor−π–donor approach (D−π–A−π–D), as allows for control of photophysical resulting through modulation highest occupied molecular orbital (HOMO) and lowest unoccupied (LUMO) energy levels. Herein, we illustrate thienothiadiazole (TTD) an effective acceptor moiety design NIR emissive fluorophores. TTD a well-known electron-deficient species, but its use D−π–A−π–D systems not extensively studied. We employed unit series two characterized experimental computational studies. Both exhibited maxima NIR-I that extends into NIR-II. also utilized electron paramagnetic resonance (EPR) spectroscopy rationalize differences measured quantum yield values demonstrated, our knowledge, first evidence radical species TTD-based small-molecule fluorophore. Encapsulation using surfactant formed polymeric nanoparticles, which were studied by morphological techniques. The results work potential NIR-II applications.