Abstract
The photophysical properties of donor (D)-acceptor (A) polymers were studied by designing two types of polymers, (D-σ-A)n and (D-π-A)n, with non-conjugated alkyl (sp3) and π-conjugated (sp2) linkers using π-extended donor and acceptor monomers that exhibit planar A-D-A structures. The non-conjugated alkyl linker provides structural flexibility to the (D-σ-A)n polymers, while the π-conjugated linker retains the rigid structure of the (D-π-A)n polymers. Photoinduced energy transfer occurs from the large donor to acceptor units in both polymers. However, the photoinduced energy transfer dynamics are found to be dependent on the conformation of the polymers, where the difference is dictated by the types of linkers between the donor and acceptor units. In solution, intramolecular energy transfer is relatively favorable for the (D-σ-A)n polymers with flexible linkers that allow the donor and acceptor units to be proximally located in the polymers. On the other hand, intermolecular (or interchain) energy transfer is dominant in the two polymer films because the π-extended donor and acceptor units in polymers are closely packed. The structural flexibility of the linkers between the donor and acceptor repeating units in the polymers affects the efficiency of energy transfer between the donor and acceptor units and the overall photophysical properties of the polymers.
Highlights
Photoinduced energy transfer or charge transfer has been extensively studied using dyad- or triadtype small molecules composed of donor and acceptor moieties (Kuss-Petermann et al, 2012; Wiebeler et al, 2017; Wang et al, 2019)
Photoinduced energy transfer in (D-σ-A)n and (Dπ-A)n in toluene is mainly due to the intramolecular energy transfer, whereas photoinduced energy transfer in the (D-σA)n and (D-π-A)n films proceeds via both intramolecular and intermolecular energy transfer. This is the first report on the photophysical properties of partially and fully conjugated polymers containing well-defined π-extended donor and acceptor monomers
Because the molecular weight of the repeating units consisting of the large monomers is over 5,000 g/mol, the molar ratio of the (D-σ-A)n and (D-π-A)n repeating units was determined to be 1:1 from nuclear magnetic resonance (NMR) spectra and theoretical elemental analyses (EA) calculations
Summary
Photoinduced energy transfer or charge transfer has been extensively studied using dyad- or triadtype small molecules composed of donor and acceptor moieties (Kuss-Petermann et al, 2012; Wiebeler et al, 2017; Wang et al, 2019). Our group reported polymer solar cells with two different copolymers synthesized by connecting conjugated donor- and acceptor-based macromolecular units (Lee et al, 2017). Donor- and acceptor-based macromolecular units were connected using sp and sp linkers, respectively, to investigate the performance of polymer solar cells. The photoinduced energy transfer and photoinduced electron transfer in the polymers can be reliably studied by using the polymers with donor- and acceptor-based macromolecular units having a uniform molecular weight. Photoinduced energy transfer in (D-σ-A)n and (Dπ-A)n in toluene is mainly due to the intramolecular energy transfer, whereas photoinduced energy transfer in the (D-σA)n and (D-π-A)n films proceeds via both intramolecular and intermolecular (or interchain) energy transfer This is the first report on the photophysical properties of partially and fully conjugated polymers containing well-defined π-extended donor and acceptor monomers. Because the molecular weight of the repeating units consisting of the large monomers is over 5,000 g/mol, the molar ratio of the (D-σ-A)n and (D-π-A)n repeating units was determined to be 1:1 from NMR spectra and theoretical EA calculations
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