In Nature, energy and electron transfer processes in the photosynthetic machinery following light absorption have been perfectionated. To mimic the aforementioned, that is, efficiently utilizing light to separate charges and, in turn, to generate solar fuels, a great variety of multicomponent artificial photosynthetic systems have been designed and synthesized. Incentives for the design build around molecules have been taken from Nature: For example, implementing suitable electrochemical gradients across arrays of several molecular building blocks have enabled the unidirectional transformation of solar energy into electrical energy. A key parameter is the right balance between the reduction / oxidation strengths of the individual building blocks and their spatial arrangements. Both affect the thermodynamic driving forces for each step and, in turn, the overall efficiency. Notably, acceptor-donor₁-donor₂ or acceptor-donor₁-donor₂-donor₃ types of artificial photosynthetic systems have been reported. Besides an initial charge transfer, charge shifts take place via oxidative electron transfers from donor₁ to donor₂ and, eventually, to donor₃.

Considering the effectiveness of multicomponent systems, in which photoexcitation triggers a cascade of short range electron transfers, we report on two sets of novel multicomponent DA₁A₂s – Figure 2. These DA₁A₂ types feature electron transport chains with C₆₀ and C₇₀ of different electron acceptor strengths to create an electrochemical gradient. As a complement to electron accepting C₆₀ / C₇₀ either zinc porphyrins (ZnP) and zinc phthalocyanines (ZnPc) were employed. The motivation for our pump-probe investigations was to establish the role of ZnPc or ZnP as light harvester and electron donor to power unidirectional (reductive) charge shift reactions along a variety of electron transport chains.

In summary, we will demonstrate the control over unidirectional charge shift along electron transport chains en route towards highly energetic, long-lived charge separated states. Key is, however, a charge shift mediating state, whose relative energy determines the overall efficiency. If the energy of the mediating state, on one hand, is higher than the charge separated state, resonance conditions enable efficiencies as high as 50%. If the energy, on the other hand, is lower than the charge separated state, deactivation to the ground state limits the efficiency to 10%.