Femtosecond dynamics and stimulated emission from the S2 state of a liquid crystalline trans-azobenzene

The excited-state S2 dynamics of an azobenzene derivative, trans-BMAB, was investigated in solution by femtosecond transient absorption and picosecond single-photon timing fluorescence spectroscopies. The fluorescence was observed at 400 nm with a lifetime ∼250 fs. The S1 state with an absorption maximum at 410–415 nm was formed with a time constant of ∼250 fs from the S2 state followed by relaxation with a lifetime of ∼2.3 ps in n-hexane. The stimulated emission from the S2 state overlapped with the femtosecond transient absorption spectra just after excitation, which was confirmed by polarization absorption spectroscopy.