ABSTRACT

The unique photophysics of π-conjugated polymers nourished a remarkable diversity of experimental as well as  theoretical approaches to reveal the mechanistic pathways of generation and the subsequent relaxation of optical excitations in this class of materials. In light of the racy development of pulsed laser instrumentation, various methods of ultrafast time-resolved spectroscopies appear as ideal experimental tools to study the nature and dynamics of excited states in conjugated macrosystems, In this contribution, after a general introduction, we discuss the meanwhile widely accepted molecular exciton picture of optical excitations in organic semiconductors in more detail, focusing on the theoretical framework for the description of incoherent excitation energy transfer, that plays the key-role in the photodynamics of conjugated  polymer systems on late femtosecond (fs) to picosecond (ps) time-scales. In this context, a specific approach developed by our Carlo method with a dynamical algorithm for solving the energy-space transport Master Equation (ME). After a brief review of experimental findings of time-resolved luminescence studies up to now, we further present an investigation on the fs relaxational dynamics of optical excitations in the model system poly-(p-phenylenevinylene) (PPV) under selective excitation/detection conditions. The dependence of luminescence kinetics on distinct, initial excitation boundaries, measured by applying the up-conversion technique, reveals a pronounced site-energy memory effect as one of the characteristic features of the hierarchically constrained multilevel relaxation in the disordered PPV many-body system. We finally close the article with an outlook on likely trends in future studies.