Ultrafast femtosecond relaxation processes in luminescent and nonluminescent conducting polymers

We have employed the time-resolved photomodulation (PM) technique to study the photoexcitation dynamics of a luminescent (Si-PT) and nonluminescent (s-(CH)x) conducting polymers in the low signal limit. In each polymer, we identify two exponential decay processes in the PM decay, with characteristic time constants T1 and T2, where T1 is of order 1 ps and T2 depends on the specific polymer; T2 in Si-PT is about 50 ps, whereas T2 in s-(CH)x is about 5 ps. The difference in T2 is tentatively attributed to radiative and non-radiative recombination kinetics, respectively. We also found that the PM decay does not show any obvious temperature and intensity dependences, whereas the polarization memory decay is longer at low temperatures.