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Figure 3: Spectroscopic properties of polyspirobifluorene indicating the optical features used in the measurement of the singlet generation ratios. Absorption (a), electroluminescence (b), electrophosphorescence (c), and transient triplet absorption spectra (d). The vertical lines indicate the energies of the optical excitation and the transient absorption probe, respectively, and the inset shows the repeat unit of the polyspirobifluorene.