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

The 1Bu 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 Ag 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.