Fast and Reliable Measurement of Photoluminescence Quantum Yields for the Development of Fluorescent Probes

Abstract

Besides molar absorption coefficient and excited state lifetime, the photoluminescence quantum yield is the key parameter to be optimized for highly efficient and bright fluorescent probes. An easy and reliable way to determine the quantum yield is therefore the prerequisite for modern fluorescent probe development.Photoluminescence quantum yield measurements are typically done by comparing the emission intensity of the target compound with a standard of known quantum yield, under identical measurement conditions. This method is well established and precise, but also time consuming. In addition target compound and reference have to have similar absorption and emission spectra. For those cases where a suitable standard is not available; when the measurement of the absorption is cumbersome, when the determination speed is an issue, or generally for scattering samples, the use of an integrating sphere to measure the absolute photoluminescence quantum yield is mandatory.Here we show that absolute photoluminescence quantum yield measurements of solutions as well as solid samples can be easily realized using a simple integrating sphere accessory for a conventional fluorescence lifetime spectrometer. This allows to acquire all relevant fluorescence characteristics with one instrument, therefore streamlining the characterization workflow and keeping all calibration schemes simple.For the validation of our new assembly, selected quantum yield standards have been measured and the data were compared to literature data previously determined with a calibrated spectrofluorometer and two calibrated integrating sphere setups [1]. Procedures for the determination of the instrument's spectral sensitivity and attainable precision of the results will be discussed.[1] Wurth, C.; Pauli, J.; Lochmann, C.; Spieles, M.; Resch-Genger, U. Anal. Chem. 2012, 84, 1345-1352.