Based on these results, we can select organic solvents with low to medium polarity to prepare a TPE-BBT solution as new PLQY standards for NIR-II materials. Due to concerns that the high brightness of the toluene solution could introduce significant errors when testing low-brightness samples, we opted to utilize THF as the solvent for this study. Generally, for relative PLQY testing, it is necessary to keep the absorbance at the excitation wavelength between 0.01 and 0.1. Figure shows that the molecular concentration range needed for this absorbance range is approximately 10-100 µM. After normalizing the absorption spectra at this concentration range, there are no noticeable changes in the absorption spectrum, indicating no dye aggregation or new species formation (Figure ). Subsequently, we examined the PLQY changes of the TPE-BBT solution within this concentration range and found negligible concentration-dependent PLQY changes at room temperature (Figures and). The mean PLQY of the TPE-BBT solution reaches 4.17% on the integrating sphere, which is even higher than that of the nanoparticle form. The excitation wavelength was then switched to 730 nm to further prove the PLQY value (Figure ). The results indicate that the measurements are very close to those obtained with 808 nm excitation, which further validates the reliability of this PLQY value (Figure ). It is noteworthy that TPE-BBT exhibits excellent shelf stability. We prepared the solid powder that had been on the shelf for two years into an organic solution and measured the absorption spectrum, finding that the spectral results were unchanged from the tests conducted two years ago (Figure ). All these results prove that the THF solution of TPE-BBT can act as a PLQY standard for the precise measurement of relative PLQY in the NIR-II window. The TPE-BBT solution was then used as the reference material for the relative PLQY measurement. The operation procedure is shown in Figure . We first prepared a TPE-BBT stock solution of about 1 mM using THF and then further diluted it with THF to achieve a concentration of 10-100 µM. Subsequently, UV-Vis spectroscopy is used to confirm that the absorbance of these TPE-BBT solutions at 808 nm was within the range of 0.01-0.1. These absorbance values should be accurately recorded. Since the absolute PLQY of these samples can be accurately measured using an integrating sphere in previous experiments, they can be used as PLQY standards. Then, relative PLQY measurement can be conveniently conducted using a PL spectrometer and the calculation equation, which helps to accurately study samples with low PLQY or when no integrating sphere setup is available. Through a process similar to TPE-BBT, the test samples are prepared into a series of solutions with absorbance at 808 nm within the range of 0.01-0.1. It is important to note that due to the different molar absorptivities of different materials, the molecular concentrations of the sample and reference may differ significantly, and the absorbance of the NIR-II sample must be strictly determined based on absorbance. Next, a PL spectrophotometer will be used to measure the spectra of the TPE-BBT solution and the NIR-II sample solution under identical conditions. As the emission peak wavelengths of the samples may differ, ensure that the correction is applied to the PL spectrophotometer. Then, calculate the ratio of the linear relationship between the spectral integral As a demonstration, we used this procedure to measure the relative PLQY of two NIR-II dyes, namely IR-26 and IR-1061 (Figure ). These two molecules are commonly used for relative PLQY measurement for 808-nm excitable NIR-II materials. Many researchers have attempted to measure their absolute PLQYs, but due to their low brightness, it has been difficult to reach an accurate conclusion. This results in a significant deviation of the relative PLQY from the actual PLQY value, thus losing its physical significance. Herein, we use TPE-BBT as a reference to measure the relative PLQY of IR-26 and IR-1061. On the one hand, this can verify the reliability of TPE-BBT as a new PLQY standard. On the other hand, it can provide new insights into the absolute PLQY of IR-26 and IR-1061, making the relative PLQY calculated based on them have practical physical significance and comparability. This will greatly promote the development and communication in the field of NIR-II materials. Figures demonstrate the PL spectra of TPE-BBT (THF solution), IR-26 (DCE solution), and IR-1061 (DCM solution), respectively. All measurements ensure that the absorbance of the samples at 808 nm is approximately between 0.01 and 0.1, and these absorbance values are accurately recorded. After calculating the slope of the linear relationship between the integrated fluorescence intensity and absorbance, we can calculate the PLQY of IR-26 to be 0.0301% and IR-1061 to be 0.193% by substituting the PLQY value of TPE-BBT as 4.17% (Figure ). We think this test result is reliable because when we substitute the new value of IR-26 into the relative PLQY calculation, the significant discrepancy between the absolute and relative PLQY in our previous work is greatly reduced. In that work, the absolute PLQY of TPE-BBT nanoparticles is 1.8%, while the relative PLQY is 31.5%, using IR-26 as a reference of 0.5%. The relative PLQY of TPE-BBT nanoparticles would be 1.9% when substituting the PLQY value of IR-26 as 0.0301%, matching well with the absolute value.