It is challenging to develop molecular fluorophores in the second near-infrared (NIR-II) window with long wavelength emission and high brightness, which can improve the performance of biological imaging. Herein, we report a molecular engineering approach to afford NIR-II fluorophores with these merits based on fused-ring acceptor (FRA) molecules. Dioctyl 3,4-propylenedioxy thiophene (PDOT-C8) is utilized as the bridging donor to replace 3-ethylhexyloxy thiophene (3-EHOT), leading to more than 20 times enhancement of brightness. The nanofluorophores (NFs) based on the optimized CPTIC-4F molecule exhibit an emission peak of 1,110 nm with a fluorescence quantum yield (QY) of 0.39% (QY of IR-26 is 0.050% in dichloroethane as reference) and peak absorption coefficient of 14.5 × 10⁴ M⁻¹cm⁻¹ in aqueous solutions, which are significantly higher than those of 3-EHOT based COTIC-4F NFs. It is found that PDOT-C8 can weaken intermolecular aggregation, enhance protection of molecular backbone from water, and decrease backbone distortion, beneficial for the high brightness. Compared with indocyanine green with same injection dose, CPTIC-4F NFs show 10 times higher signal-to-background ratio for whole body vessels imaging at 1,300 nm long pass filters.

在第二个近红外（NIR-II）窗口中开发具有长波长发射和高亮度的分子荧光素具有挑战性，这可以提高生物成像的性能。在这里，我们报告了一种分子工程方法，以基于稠环受体（FRA）分子的这些优点提供NIR-II荧光团。使用二辛基3,4-丙二氧基噻吩（PDOT-C8）作为桥接供体来取代3-乙基己氧基噻吩（3-EHOT），可将亮度提高20倍以上。基于优化的CPTIC-4F分子的纳米荧光团（NFs）表现出1,110 nm的发射峰，其荧光量子产率（QY）为0.39％（在二氯乙烷中IR-26的QY为0.050％），且峰吸收系数为14.5×10 ⁴ M ^-1厘米^-1在水溶液中，显着高于基于3-EHOT的COTIC-4F NFs。发现PDOT-C8可以减弱分子间聚集，增强分子骨架对水的保护，并减少骨架畸变，有利于高亮度。与相同注射剂量的吲哚菁绿相比，CPTIC-4F NFs在1300 nm长通滤光片上成像的全身血管的信噪比高10倍。