TIPS-Pn (Ossila) and TIPS-Tn (Lumtec) were used as received. 8 mM and 0.05 mM solutions of each were prepared in anhydrous toluene (Sigma-Aldrich) in a glovebox under a nitrogen atmosphere. The O 2 content was kept below 0.5 ppm. Steady-state absorbance spectra were recorded on a Cary Varian 1E UV-visible spectrophotometer (supplementary material Sec. 2). The pathlength used for spectroscopic measurements was 0.03 mm for the 8 mM samples and 2 mm for the 0.05 mM samples. Transient absorption spectroscopy measurements were conducted on a home-built instrument, using the 1030 nm output of a pulsed laser operating at a 5 kHz repetition rate (Light Conversion, Pharos). A portion of the output was doubled to 515 nm and introduced to a home-made optical parametric amplifier to obtain 810 nm, which was doubled to a 405 nm pump beam. The probe was a white light continuum obtained by focusing a portion of the 1030 nm output onto a 1 cm pathlength cuvette of D 2 O. The white light continuum was then focused onto the sample with a 0.2 mm spot size, and detected with a spectrograph (Oriel, 77400) and camera (Andor, Zyla 5.5 sCMOS). Experiments were performed with the pump polarization rotated to the magic angle (54.7 • ) relative to the probe. Data were taken at pump powers of 3.8 mW (0.76 µJ) and 2 mW (0.4 µJ), for which no power dependence was observed. Photo-degradation was observed to be less than 10% after each experiment.