2.4. Time-Correlated Single Photon Counting

Time-correlated single photon counting (TCSPC) measurements were conducted using a FluoTime 250 fluorescence spectrometer (PicoQuant, Berlin, Germany). The solutions were excited at 405 nm and emission was collected at ~500 nm, which corresponded to the peak emission intensity of the solutions. The instrument response function (IRF) was determined to be ~80 ps by measuring scattered light from a solution of colloidal silica (i.e., Ludox) located at the sample position. The sample solutions were diluted from their original concentration of 4 μM such that their maximum absorbance was 0.1 in the range of 350 to 500 nm.