Therefore, the documented QY values of the references would have large deviations, and there is a discrepancy among the documented QY values for the same reference. Thus, the measurement of relative QYs for NIR-II dyes is not accurate. Based on the ultrahigh QY of TPE-BBT, we precisely measured its absolute QY in different states using an integrating sphere (Table ). Compared to the undetectable absolute QY of TPA-BBT PLNPs, the absolute QY of TPE-BBT PLNPs was detected to be 1.8%, which was an extremely high value for NIR-II dyes. According to the changes in PL intensity in different water fractions (f w ), TPE-BBT demonstrated a sharp increase in PL intensity at the f w = 20%, and the PL intensity gradually decreased afterwards. The size distributions and morphologies of TPE-BBT nanoaggregates at f w = 20%, 50%, and 99% were characterized by dynamic light scattering (DLS) and scanning electron microscope (SEM), respectively (Figures and). TPE-BBT began to form large aggregates with a mean diameter (d) of 629 nm at f w = 20%, and the size of formed aggregates decreased when the f w increased to 50% (d = 203 nm) or 90% (d = 82 nm). The absolute QYs of three aggregates in different f w were measured. The largest aggregates at f w = 20% showed the highest QY of 4.6%, while smaller aggregates displayed reduced QY values of 3.4% at f w = 50% and 2.1% at f w = 99% (Figure ). This phenomenon suggested that the QY of TPE-BBT was related to the size of aggregates.