In this paper, we theoretically investigated external electric field-dependent photoinduced charge transfer (CT) in a donor–acceptor (D-A) system in two-photon absorption (TPA) where PCDTBT and PC70BM were selected as the D and A, respectively. Using our developed visualization methods, we can directly observe the dynamic processes of photoinduced CT in each step in different transition channels in TPA with two-dimensional transition density matrix and three-dimensional charge difference density. Our results revealed that the strong absorption peaks in TPA can be resulted from intermolecular charge transfer transitions where the first step transition in TPA is the localized excited state with strong absorption and the second step transition in TPA is the intermolecular charge transfer excited state. The intensity ratio of intermolecular charge transfer in strong absorption peaks in TPA will be controlled by an external electric field where the absorption peak of charge transfer characterization in TPA can be reached up to about 90% with an optional external electric field. Our results can promote deeper understanding optical properties of the D-A system in TPA and provide a method for increasing the ratio of intermolecular charge transfer excited states in TPA.

In this paper, photoinduced intermolecular charge transfer (PICT) and fluorescence resonance energy transfer (FRET) in donor-acceptor systems have been investigated experimentally and theoretically. We attempt to investigate the natural relationship between FRET and PICT, and reveal the advantages of FRET enhanced PICT. The driving force for PICT in the FRET system equals the reorganization energy, which gives barrier-less charge transfer according to Marcus theory. The rates of PICT in the FRET system can be estimated with our simplified Marcus equation. Our results can promote the deeper understanding of the nature of FRET enhanced PICT, and benefit rational design for the use of the FRET system in organic solar cells.

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In this review, we firstly introduce physical mechanism of fluorescence resonance energy transfer (FRET), the methods to measure FRET efficiency, and the applications of FRET. Secondly, we introduce the principle and applications of plasmon‐enhanced fluorescence (PEF). Thirdly, we focused on the principle and applications of plasmon‐enhanced FRET. This review can promote further understanding of FRET and PE‐FRET.

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