Monomolecular triplet decay dynamics in fluorene-based conjugated polymer films studied by transient absorption spectroscopy

Monomolecular decay dynamics of triplet excited states formed in fluorene-based conjugated polymer pristine and blend films were studied by transient absorption spectroscopy over the temperature range 77–300 K. The decay rate was temperature independent below 150 K and steeply increased above 150 K. The temperature dependence from 150 to 300 K was expressed by the Arrhenius equation with an activation energy of 0.12 eV. The thermal activation process was assigned to the temperature-dependent non-radiative decay of triplet excitons, which might result from the spin–orbit coupling enhanced by vibrational motions in F8BT. The same tendency was observed for blend films, although with slightly faster decay dynamics, suggesting that the thermal activation process reflects an intrinsic photophysical property of the fluorene-based polymer.