Abstract
The lowest excited singlet state (S1) of 4,4′-bipyridine (44BPY) has been studied in water
and methanol by using pump-probe time-resolved resonance Raman spectroscopy in the
picosecond time domain. Spectroscopic evidence for a disymmetric S1 structure with
localization of the electronic excitation in one of the two pyridyl rings is given. The fast
formation of the N-hydro radical 44BPY