Femtosecond spectroscopy of a polydiacetylene with extended conjugation to acetylenic side groups

Femtosecond pump-probe measurements have been performed for a polydiacetylene (PDA), [bis-(N-butoxycarbonylmethyl)carbamate] (PDA-5BCMU-4A), which lacks steric hindrance among the straight side groups resulting in the most delocalized π-electrons among PDAs ever studied. The lifetime of the induced absorption increases with decreasing temperature from 0.92 ps at 290 K to 1.08 ps at 10 K. The risetimes of the induced absorption just below the stationary absorption are between 100 and 400 fs, depending on the probe wavelength at all temperatures studied (290-10 K). The relaxation scheme can be given by 11Bu free exciton → {100–400 fs (wavelength dependent)} quasi-thermal 21Ag state → {1.08 ps (10 K)−0.92 ps (290 K)} 11Ag ground state.