Confined breather-type excitation in a quinoidal thiophene after sub-5 fs pulse excitation

摘要

A quinoidal thiophene molecule which is a prototype of the repeated unit of s-tran-cis-polyacetylene was studied by sub-5 fs spectroscopy.A breatherlike mode modulation of both the amplitude and frequency of the C=C stretching was observed for the first time.It generates two sidebands of 2238 and 700 cm~(-1)with a separation of 769 cm~(-1)corresponding to the modulation frequency.The latter mode is very close to the C-S-C ring deformation,which indicate that this mode mediates coupling between the breather mode and the C_(beta)-C_(beta)stretching mode.It was also found that the breather-type excitation has a longer lifetime (2-3 ps)than in all-trans-polyacetylene (50 fs)due to its confinement.