Synthesis And Properties Of D-A Polymers Based On Benzodipyrrolidones

In recent years, as organic solar cell (OSC) materials developed rapidly, more and more attention has been focused on the research to improve the OSC’s light-absorbing properties and monochromatic incident photon-to-electron conversion efficiency (IPEC). The wavelength spectrum of the light, which is absorbed by light-absorbing materials of OSC, should cover the visible region as widely as possible. Polymeric materials with narrow band gaps show outstanding advantages in absorbing both the short and the long wavelength or even near infrared light. There are two strategies to lower the energy gap of the polymers:enhance the donor-acceptor (D-A) interactions, or enhance the π-π stacking to extend the conjugated molecular structure. In this thesis, a series of different D-A strength copolymers with low band gap were designed and synthesized based on benzodipyrrolidone, while the structures and properties of the polymers were studied systematically.(1) D-A copolymers based on BDP and carbazole derivatives. N,N-di(2-octyldodecyl)-3,7-di(4-bromopheny])-2,6-dioxo-1,2,5,6-tetrahydrobenzo[1,2-b:4,5-b’]dipyrrole (BDP) and 3,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9-octylcarbazole and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9-octylcarbazole were used as acceptor and donors, respectively, to synthesize polymer PBDP-36CZ and PBDP-27CZ. The structures of the monomers and polymers were fully characterized via 1H NMR, and Uv-vis absorption properties, electrochemical and thermal properties of the monomer and polymers were systematically investigated. The results showed that different molecular steric hindrance can have an impact on the intramolecular charge transfer (ICT), so that D-A copolymers with more stretched mainchains and slighter molecular steric hindrance would be able to demonstrate lower energy band gaps. In CHCI3, PBDP-36CZ, which has larger molecular steric hindrance than PBDP-27CZ, has a Uv-vis long wavelength absorption peak at 514nm, while PBDP-27CZ’s peak at 522nm, while the optical energy gaps of PBDP-36CZ and PBDP-27CZ were 1.85 eV and 1.82 eV, respectively. On the other hand, the interactions between BDP and carbazole derivatives enhanced the ICT properties, so that the long wavelength absorption peaks of PBDP-27CZ and PBDP-36CZ on Uv-vis spectrum redshifted 54nm and 46nm than the absorption peak of monomer BDP in CHC13.(2) D-A copolymers based on benzodipyrrolidone derivatives BDP and BDT. Two different benzodiyrrolidone monomer N,N-di(2-octyldodecyl)-3,7-di (4-bromophenyl)-2,6-dioxo-l,2,5,6-tetrahydrobenzo[l,2-b:4,5-b’]dipyrrole (BDP) and 1,5-Dihexyl-3,7-dithiophen-2-yl-1H,5H-pyrrolo[2,3-f]indole-2,6-dione (BDT) which were used as acceptors, were respectively copolymerized with thiophenal derivatives 3,4-ethoxylene dioxy thiophene (EDOT), Thieno[3,2-b]thiophene (DT) and 3,5-didoecylbisthieno[3,2-b:2’,3’-d]thiophene (DTT) to obtain polymers PBDP-EDOT, PBDP-DT, PBDP-DTT, PBDT-EDOT, PBDT-DT and PBDT-DTT. The structures of monomers and polymers were characterized by 1H NMR, and the Uv-vis absorption spectrums of the monomer and polymers, as well as the electrochemical properties of the polymers were studied in detail. The Uv-vis absorption spectrum demonstrated the long wavelength absorption of PBDP-EDOT, PBDP-DT, PBDP-DTT, PBDT-EDOT, PBDT-DT and PBDT-DTT are 589nm,591nm,600nm,679nm,705nm and 828nm, respectively, and the electrochemical band gaps of PBDP-EDOT, PBDP-DT, PBDP-DTT, PBDT-EDOT, PBDT-DT and PBDT-DTT are 1.56 eV,1.52 eV,1.43 eV,1.39 eV,1.30 eV and 1.16 eV, which showed that as the electron-withdrawing abilities enhanced from BDP to BDT, as well as the electron-donating abilities increased from EDOT to DTT, ICT of polymers increased from PBDP-EDOT to PBDT-DTT.(3) Derivatives of benzodipyrrolidone BDP and BDP-T were reacted with 4’-(4-pinacolatoboronphenyl)-2,2’:6’,2"-terpyridine via Suzuki coupling to obtain PBDP-TPY and PBDP-T-TPY, the monomers were self-assembled with Zn2+or Ru2+ to obtain supramolecular polymers PBDP-TPY-Zn, PBDP-TPY-Ru and PBDP-T-TPY-Ru. Optical and electrochemical properties of the monomers and supramolecular polymers were fully characterized. The long wavelength absorption peak of PBDP-TPY-Zn showed little difference with its monomer BDP-TPY, while the long wavelength absorption peak of monomer BDP-TPY was 499nm, and peak of supramolecular polymer PBDP-TPY-Ru redshifted to 519nm, and the energy gap of PBDP-T-TPY-Ru was 1.71 eV, lower than the energy gap of monomer BDP-T-TPY (2.21 eV). The results above showed that metallic ion with changeable valence has much influence on the ICT of supramolecular polymers. At the same time, due to the MLCT of Ru2+, the absorption near 400nm on the Uv-vis Absorption spectrum of PBDP-T-TPY-Ru enhanced than that of monomer BDP-T-TPY.