Fig. 1: Competing processes in excited state quenching of D–PS–A-type molecules in charge-separated states.
From: Photoinduced double charge accumulation in a molecular compound
a, Energy-wasting photoinduced charge recombination is favoured over energy-storing charge accumulation. b, Simultaneous excitation of both photosensitizer units in D–PS–A–PS–D molecules circumvents the destructive processes from a. c, The sequential excitation pattern (achievable at low irradiances) in such D–PS–A–PS–D molecules cannot lead to substantial charge accumulation. d, A general strategy for charge accumulation via sequential photon absorption at much lower irradiances. Blue arrows denote excitation with light; black horizontal arrows are simple reaction arrows. The initial electron–hole pair is stored peripherally, away from the photosensitizer. Secondary excitation of PS allows faster reaction with nearby electron donors and acceptors, despite greater driving force for unwanted light-induced charge recombination compared to light-induced charge accumulation. Legend: in general, for simplicity and comparability, reductive quenching of the excited state is shown. Depending on the actual donor and acceptor, oxidative quenching may also occur. The general principles apply to both cases.
