A Cary 100 UV-vis spectrometer (Varian) and a fluorometer Cary Eclipse (Agilent Technologies) were used for the steady state absorption and emission measurements, respectively. All the measurements were performed using 10*10 mm quartz optical cell. The time-resolved emission measurements were carried out by using the time-correlated single photon counting (TCSPC) set-up described in ref . Briefly, the excitation pulses were generated by a femtosecond Ti:sapphire laser (Coherent Chameleon Ultra II, 80 MHz, 200 fs, 3.8 W) coupled with a pulse picker (4 MHz) and a harmonic generator (SHG/THG, APE). The fluorescence lifetime measurements were carried out with the FT200 PicoQuant spectrometer and the emission signal was collected with a polarizer set at the magic-angle and a Czerny-Turner type monochromator connected to a computer for observation wavelength selection. The photons were collected with a cooled microchannel plate photomultiplier tube R3809U (Hamamatsu) and recorded using a PicoHarp 300 TCSPC system (PicoQuant). The instrumental response function (IRF) was measured using Ludox colloidal solution and the full width at half maximum (FWHM) was found to be 50 ps. For these experiments, the emission was collected at 90 degrees using a 10*10 mm optical cell. The software used to plot and process the decays was FluoFit v.4.6.6 (PicoQuant) and a home-made python script. The excitation wavelength used for each compound is given in the text.