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 T 1 and T 2 , where T 1 is of order 1 ps and T 2 depends on the specific polymer; T 2 in Si-PT is about 50 ps, whereas T 2 in s-(CH) x is about 5 ps. 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.