Spectroscopic Approach to Energetics of Exciton Fission and Fusion in Tetracene Crystals

The singlet–triplet ${\mathrm{(T}}_1{\mathrm{\hspace{0.17em}\leftarrow \hspace{0.17em}S}}_0)$ excitation spectrum for delayed fluorescence and the prompt fluorescence ${\mathrm{(S}}_1{\mathrm{\hspace{0.17em}\to \hspace{0.17em}S}}_0)$ emission spectrum have been measured for a tetracene crystal at room temperature. The origin (0–0 transition) in the two spectra at 10 100 ± 20 and 18 680 ± 30 cm⁻¹, respectively, imply the activation energy for singlet exciton fission, $\text{ΔE\hspace{0.17em}=\hspace{0.17em}1520\hspace{0.17em}±\hspace{0.17em}70}{\mathrm{cm}}^{\text{−1}}$ . Raman lines corresponding to the vibrational structure in the above spectra were detected. The fluorescence emission spectra show the need for taking reabsorption effects into account.