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

The ultrafast-relaxation kinetics of the singlet excitons in polydiacetylene 4 BCMU was measured at hydrostatic pressures up to 80 kbar, using the pump-probe photoinduced-absorption technique with 70-fs time resolution at 2 eV and 5 ps in the spectra 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 atmospehric 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 1D relaxation process, whereas th slow component is due to exciton recombination which requires a subsequent 3D distortion of the polymer chain.