A Bright Organic Fluorophore for Accurate Measurement of the Relative Quantum Yield in the NIR‐II Window

Abstract Organic dyes with photoluminescence in the second near‐infrared window (NIR‐II, 1000–1700 nm) are promising for bioimaging and optoelectronic devices. Photoluminescence quantum yield (PLQY) is a direct measure of their performance. Integrating sphere technology is effective in determining the absolute PLQY. However, the low PLQY values of most NIR‐II organic fluorophores lead to significant measurement errors. Therefore, the most common method for PLQY determination is a relative approach using a photoluminescence spectrometer and a standard reference like IR‐26. Although the relative method enables precise calculation of the PLQY ratio between the sample and the reference, the specific PLQY value of IR‐26 is not clearly defined and is reported to range from 0.05% to 0.50%. Such a deviation can cause significant errors in relative PLQY measurements. In this study, it is reported that a bright organic fluorophore called TPE‐BBT exhibits a high PLQY of 3.94% in THF, which can be accurately measured using a commercially available integrating sphere. Using TPE‐BBT as a standard, the PLQY values of IR‐26 in 1,2‐dichloroethane and IR‐1061 in dichloromethane are accurately determined to be 0.0284% and 0.182%, respectively. It is hoped that using this reliable standard will unify the evaluation criteria for NIR‐II organic fluorophores.