A bright organic fluorophore for precise measurement of the relative quantum yield in the NIR-II window

Organic dyes with photoluminescence in the second near-infrared window (NIR-II, 1000–1700 nm) are essential in bioimaging and optoelectronic devices. Photoluminescence quantum yield (PLQY) is their important performance indicator. Integrating sphere technology is effective in determining the absolute PLQY. However, the low emission brightness of most NIR-II organic fluorophores results in unacceptable errors. Therefore, the most common method for determining the PLQY is a relative approach using photoluminescence spectrometers and a standard reference like IR-26. Although the relative method can obtain accurate PLQY ratios between the samples and references, the specific PLQY value of IR-26 is not clearly defined, which is reported to range from 0.05% to 0.50%. Such a deviation can cause significant errors in relative PLQY measurements. In this study, a bright organic fluorophore called TPE-BBT exhibits a high PLQY of 4.17% in THF, which can be accurately measured using a commercially available integrating sphere. Using TPE-BBT as a standard reference, we have determined the PLQY values of IR-26 in DCE to be 0.0301% and IR-1061 in DCM to be 0.193%.