Fig. 4. Transient kinetics and spectra of different singlet fission intermediates in amorphous pentacene derivative nanoparticles. (a) Transient absorption kinetics of TSBS-, TIPS-, and TES-pentacene nanoparticles in the visible spectral region. The transient absorption kinetics were obtained at a wavelength associated with overlapping ground-state bleach and stimulated emission features. The data were normalized to the maximum signal amplitude in the vicinity of ca. 3–50 ps. (b) Triplet photoinduced absorption spectrum of solution-phase TSBS-pentacene, transient absorption spectra of the nascent triplet pair intermediates in amorphous TSBS-, TIPS-, and TES-pentacene nanoparticles, and triplet photoinduced absorption spectrum of a crystalline film of TES-pentacene. The spectra have been offset for clarity of presentation.