High-pressure effects on ultrafast-relaxation kinetics of excitons in polydiacetylene 4BCMU

Ultrafast-relaxation kinetics of the singlet excitons in polydiacetylene 4BCMU was measured at hydrostatic pressures up to 80 kbar, using the pump-probe photoinduced-absorption technique with 70-fs resolution at 2 eV and 5 ps in the spectral range 1.2-2.2 eV. The 100-fs decay component survives at high pressures, but the slow component evolves from a 1.5-ps exponential decay at atmospheric pressure to a much slower stretched-exponential decay at high pressures with a complete recovery in the ns time range. Results suggest that the fast decay component is a ID relaxation process, whereas the slow component is due to exciton recombination which requires a subsequent 3D distortion of the polymer chain.