To investigate the role of different donors, TPA-BBT, TPE-BBT, and TPEO-BBT were synthesized using TPA, TPE, and methoxyl-TPE as electron donors. Their structures were well characterized by 1 H NMR, C NMR, and high-resolution mass spectra (Figures S1S6). All three compounds possessed a typical D-A-D structure, where the benzobisthiadiazole (BBT) acted as a strong electron acceptor, and the hexyl unit at the ortho position of thiophene ensured the distorted backbones. We first evaluated the photophysical properties of TPE-BBT and TPEO-BBT. They showed high absorption at 500800 nm in DMSO, with the molar absorption coefficients larger than 1.4  10 4 M -1 cm -1 (Figure ). TPE-BBT PLNPs encapsulated by F127 showed a similar absorption and a strong PL in the region of 9001200 nm, indicating the potential application of TPE-BBT as a NIR-II imaging agent (Figure ). TPE-BBT was weakly emissive in its good solvent DMSO, but was highly emissive in aggregates formed by gradually increasing the fraction of water, suggesting its typical AIE property (Figures and). TPEO-BBT also demonstrated an obvious AIE characteristic in the DMSO/water mixture (Figure ). The absorption and emission spectra of TPEO-BBT were slightly redshifted relative to those of TPE-BBT, indicating that the electron-donating ability of methoxyl-TPE is stronger than that of TPE. The relative QYs of TPE-BBT, TPEO-BBT, and TPA-BBT in F127 PLNPs were measured using IR26 (QY = 0.5%) as the reference. TPA-BBT PLNPs exhibited a relative QY of 12.7%, which was consistent with out previous result (11%). TPE-BBT and TPEO-BBT PLNPs showed ultrahigh relative QYs of 31.5% and 23.9%, respectively, which are among the highest reported QYs in the aqueous solution (Figure ). The relatively lower QY of TPEO-BBT PLNPs resulted from the stronger D-A interaction, demonstrating the importance of the optimization of the D-A interaction.