Fluorescence emission spectra were recorded on a SPEX Fluorolog 3 fluorometer with double grating monochromators in the excitation and emission channels. Excitation light source was a Xenon lamp (450 W, Osram) and the detector was a Peltier cooled photomultiplier tube (Hamamatsu, R636-10). The fluorescence emission signal is collected in a right-angle geometry, and the fluorescence spectra are corrected for fluctuations of the excitation source flux. For the singlet oxygen emission at 1275 nm, a highly sensitive liquid nitrogen cooled InGaAs detector (Electro-Optical Systems DSS series cryogenic receiver, 2 mm InGaAs photodiode) was coupled to a Horiba Jobin Yvon Spex Fluorolog 3 spectrofluorometer. Maximum slits (excitation and emission) and long integration times (10 -15 s) were used. A 850 nm cut-off filter was used in the emission path, to prevent second order effects of the fluorescence compounds. Triplet state lifetimes were determined by nanosecond timeresolved absorption spectroscopy using an EKSPLA NT342B laser system in which the third harmonic of a Nd:YAG laser system was used to pump an optical parametric oscillator (OPO) at the corresponding excitation wavelengths for each experiment. The typical power was 1 -2 mJ per pulse and the laser system was operated at 5 Hz. Probe light, running at 10 Hz, was generated using a high-stability short arc xenon flash lamp (FX-1160, Excelitas Technologies) with a PS302 controller (EG&G). The probe light was split in a signal and a reference beam with a 50/50 beam splitter and focused on the entrance slit of a spectrograph (SpectraPro150, Princeton Instruments). The signal beam (A = 1 mm 2 ) was passed through a sample cell and overlapped with the excitation light on a 1 mm × 1 cm area, perpendicular to the excitation beam. A reference beam was used to normalize the signal for fluctuations in the flash lamp intensity. Both beams were recorded with an intensified CCD camera (PI-MAX3, Princeton Instruments) using 5 -20 ns gate depending on the time steps of the measurements. The timing was achieved with a delay generator 6 (DG535, Stanford Research Systems, Inc.) and the setup was controlled with an in-house written program (LabView). Time-resolved fluorescence decays were measured using a TCSPC technique. The relevant excitation wavelengths were generated by frequency doubling of the output of a tunable Titanium:Sapphire laser (Chameleon Ultra, Coherent). The repetition rate is decreased from the fundamental 80 MHz to a lower value (usually 8 MHz) using a pulse picker (Pulse Select, APE). The fluorescence was detected with a multichannel plate photomultiplier tube (R3809U-50, Hamamatsu) through a single-grating monochromator (Newport Cornerstone 260, f = 250 mm, grating 300 ln/mm blaze 422 or grating 300 ln/m blaze 750 nm M20, Carl Zeiss, 600 lines/mm). The overall instrument response is usually 20 -25 ps (FWHM) measured from a dilute scattering solution (Ludox) at the excitation wavelength. TCSPC histograms were recorded using ~10 4 counts in the peak channel using the SPCM program (Becker & Hinkle).