Ultrafast femtosecond relaxation processes in luminescent and nonluminescent conducting polymers

We have employed the time-resolved photomodulation (PM) technique to study the photoexcitation dynamics in 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 T] and where T] is of order 1 ps and T2 depends on the specific polymer; T 2 in Si-PT is about 50ps, whereas T 2 in s-(CH)x is about 5ps. The difference in T 2 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.