Dynamics of singlet exciton in 1D conjugated polydiacetylene chains: a femtosecond fluorescence study

摘要

The ~1B_u exciton lifetime has been measured in isolated polydiacetylene chains, using fluorescence up-conversion. It is found to be 130-135 fs at 20 K, and corresponds to the non-radiative internal conversion to a lower-lying excited A_g state, as in polyenes. At low temperature, the absorption linewidth is almost lifetime-limited: inhomogeneous broadening is small (<= 30 cm~(-1)). The lineshape remains Lorentzian up to 150 K, but with a three-fold increase in width, whereas the lifetime is merely constant. The broadening is most probably due to a reduction of the coherence time.