Fluorophores that exhibit second near-infrared (NIR-II, 1000-1700 nm) emission play a crucial role in materials sciences. As NIR-II emission experiences reduced scattering and better penetration, these fluorophores are extremely valuable in advanced applications like fluorescent probes, sensors for medical diagnostics, phototheranostics, organic light-emitting diodes, communication technologies, and information security displays. Compared to their inorganic counterparts, organic fluorophores offer advantages such as higher biosafety, lower cost, more tunable optical properties, and better environmental friendliness. Furthermore, they have well-defined chemical structures, ensuring satisfactory repeatability for the basic research on NIR-II applications. One key parameter that determines the performance of organic fluorophores is the photoluminescence quantum yield (PLQY), which is defined as the ratio of the number of emitted photons to the number of absorbed photons: 𝛷 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝ℎ𝑜𝑡𝑜𝑛𝑠 𝑒𝑚𝑖𝑡𝑡𝑒𝑑 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝ℎ𝑜𝑡𝑜𝑛𝑠 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 (1) This quantity evaluates the photoluminescence (PL) efficiency and guides the selection of organic emitters. Due to the inevitable bathochromic absorption and emission, NIR-II fluorophores typically have a narrow band gap, which results in a low PLQY. As an optimized optoelectronic performance is of central importance for developing new NIR-II materials, the determination of PLQY is becoming essential in the photophysical and mechanistic study of every NIR-II organic fluorophore.