Resolving Energy and Electron Transfer Processes in Dyads With the Help of Global and Target Analysis

In any photosynthetic/photocatalytic device, multiple steps are required between the arrival of a solar photon and the formation of a stable product. Here we explain and demonstrate the target analysis methodology to develop minimal models, identify the steps and estimate the parameters that characterize energy converting devices. With this modelling tool the molecular mechanisms of the loss processes can be identified and quantified. This can then inspire photosynthetic device optimization by precisely targeting those sites involved in the most significant losses. Two case studies of recently published measurements (Pillai et al., 2013) on a carotenoporphyrin dyad and a carotenofullerene dyad are modelled in depth. After carotenoid excitation, no excited state energy transfer (EET) to porphyrin was found, but EET from carotenoid hot S1 to the fullerene moiety occurred with a rate of 1.6/ps. The total radical pair yields of these dyads were found to be, respectively, 46% and 79%. Out of these 79%, 31% were due to electron transfer from the fullerene excited state. The triplet yields were 3.8% and 4.6%. The remainder of the excitations decay to the ground state from the carotenoid hot S-1 and S-1 states.