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

Abstract

A quinoidal thiophene molecule which is a prototype of the repeated unit of s-trans-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. (c) 2006 American Institute of Physics.