Influences of interchain interaction on exciton dynamics in poly(3-alkylthiophene)

Luminescent conjugated polymers, poly(3-alkylthiophene) (PAT) with alkyl side chains of different lengths have been studied using tune-resolved photoluminescence (PL) spectroscopy. PL characteristics in polymer films of PAT with a long alkyl side chain are found to depend on the preparation methods of the films, namely spin coating and casting methods. The PL spectrum of the cast film is redshifted with respect to that of the spin-coated film. PL decays of both films follow single exponential function. However, it is found that the cast film has a longer PL lifetime with a lower PL efficiency in comparison to the spin-coated film. PL characteristics are also found to depend on the length of the side chains. In PAT with a short alkyl side chain, PL decay does not follow a simply single exponential function, but obeying a suppressed-exponential function. PL lifetime and quantum efficiency increase with increasing length of the side chains. The experimental results have been discussed by taking the interchain interaction as the result of the exciton dissociation at strongly interacted chains and the formation of nonemissive interchain species such as polaron pairs into consideration.