Probing of the 2Ag state in nanopolyacetylene on the time scale from femtoseconds to milliseconds

The dynamic properties of the 2Ag state in films of nanopolyacetylene have been measured using photoinduced spectroscopy and photoinduced polarimetry methods both in the transient and cw regime. The excitation density per polyacetylene nanoparticle was no more than one absorbed pump photon. Using femtosecond pulses, we evaluated the rise time (≤0.2 ps) and the decay time (≈1 ps) of the photoinduced response from the 2Ag state of trans-nanopolyacetylene. The longest relaxation time ≈7 μs was measured at room temperature. Using picosecond pulses and a novel photoinduced polarimetry method, we have done the first measurements of the transient polarization response of a conjugated material. The observed polarization signal is associated with a small photoinduced dichroism and birefringence in the 2Ag state. The decay time of the polarization signal was ≈0.3 ns.