In order to get a better insight of the S1 state of Pyr2Bpy and also on its reaction with TEOA, femtosecond transient absorption spectra (TAS) of Pyr2Bpy were recorded in THF (Figure . The transient spectra recorded for pump-probe delays shorter than 150-200 fs are dominated by the contribution of the impulsive response of the solvent. After 200 fs the transient spectra show two negative bands in the spectral range below 500 nm. The first band is formed in less than 200 fs and it exhibits a maximum at 360 nm that corresponds to the S0 → S1 absorption band (Figure ). This contribution is due to the bleaching of the ground state of Pyr2Bpy, i.e. the decrease of the absorption due to the depopulation of the ground state upon the photoexcitation. We notice in Figure , and notably in the kinetic trace reconstructed for probe = 360 nm, that the amplitude of the bleach signal is constant during the first picosecond, indicating that there is no ultrafast internal conversion involved in the photophysical process of Pyr2Bpy in THF. The maximum of the second negative shifts continuously from ca. 400 nm to 450 nm during the two first picosecond. The final position with a maximum close to 450 nm is in good agreement with the emission band (Figure ) and therefor, this band is assigned to the excited-state stimulated emission of the S1 state of Pyr2Bpy. In the spectral range above 400 nm, the transient spectra exhibit a strong, broad and slightly structured absorption band with a maximum peaking above 700 nm that characterize the absorption of the S1 state. In the kinetic traces between 150 fs and 1 ps, the formation of the excited state absorption band occurs concomitantly with the spectral shift of the stimulated emission illustrated for probe = 400 nm and probe = 450 nm. On the longer timescale, from 1 ps to 1500 ps (Figure ) the shape of the transient spectra does not change, only the amplitude of the signal decreases, resulting in an isobestic point at 530 nm. The decay of the signal is not completed after 1.5 ns, in good agreement with the lifetime deduced from the TCSPC data. The transient spectra evolution reveals the decay of the excited state without any spectral signature of the conversion of the S1 state into a new transient species. Thus, the internal conversion from the S1 to the S0 state by emission represents the main relaxation channel of Pyr2Bpy.