Abstract
Photoinduced charge separation in donor–acceptor conjugates plays a pivotal role in technology breakthroughs, especially in the areas of efficient conversion of solar energy into electrical energy and fuels. Extending the lifetime of the charge separated species is a necessity for their practical utilization, and this is often achieved by following the mechanism of natural photosynthesis where the process of electron/hole migration occurs distantly separating the radical ion pairs. Here, we hypothesize and demonstrate a new mechanism to stabilize the charge separated states via the process of electron exchange among the different acceptor entities in multimodular donor–acceptor conjugates. For this, star-shaped, central triphenylamine derived, dimethylamine–tetracyanobutadiene conjugates have been newly designed and characterized. Electron exchange was witnessed upon electroreduction in conjugates having multiple numbers of electron acceptors. Using ultrafast spectroscopy, the occurrence of excited state charge separation, and the effect of electron exchange in prolonging the lifetime of charge separated states in the conjugates having multiple acceptors have been successfully demonstrated. This work constitutes the first example of stabilizing charge-separated states via the process of electron exchange.
Highlights
Understanding the principles governing the kinetics of charge transfer and separation, securing high charge separation quantum yields, avoiding large energy losses, and prolonging the lifetime of the radical ion pairs by molecular engineering of the conjugates have been the main focus of these studies.[1,2,3,4,5,6,7,8,9,10,11,12]
We have developed exceptional molecular donor– acceptor systems consisting of C3 symmetric central triphenylamine derived, dimethylamine–tetracyanobutadiene conjugates
Frontier LUMO energy levels and orbital coefficients helped us in rationalizing such electron exchanges
Summary
Excited state charge transfer in donor–acceptor conjugates is one of the widely investigated topics in recent years due to their usage in building energy harvesting photonic devices.[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] Understanding the principles governing the kinetics of charge transfer and separation, securing high charge separation quantum yields, avoiding large energy losses, and prolonging the lifetime of the radical ion pairs by molecular engineering of the conjugates have been the main focus of these studies.[1,2,3,4,5,6,7,8,9,10,11,12] In simple donor– acceptor conjugates, charge separation from the excited singlet state of the donor or acceptor can store the greatest amount of energy; since the process originates from the singlet excited state, the charge separated states are generally short-lived. We hypothesize and demonstrate a new mechanism to stabilize the charge separated states via the process of electron exchange among the different acceptor entities in multimodular donor–acceptor conjugates.
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