Organic Donor-Acceptor Systems for Photocatalysis

Abstract

Organic semiconductor materials are considered to be promising photocatalysts due to their excellent light absorption by chromophores, easy molecular structure tuning, and solution-processable properties. In particular, donor-acceptor (D-A) type organic photocatalytic materials synthesized by introducing D and A units intra- or intermolecularly, have made great progress in photocatalytic studies. More and more studies have demonstrated that the D-A type organic photocatalytic materials combine effective carrier separation, tunable bandgap, and sensitive optoelectronic response, and are considered to be an effective strategy for enhancing light absorption, improving exciton dissociation, and optimizing carrier transport. This review provides a thorough overview of D-A strategies aimed at optimizing the photocatalytic performance of organic semiconductors. Initially, essential methods for modifying organic photocatalytic materials, such as interface engineering, crystal engineering, and interaction modulation, are briefly discussed. Subsequently, the review delves into various organic photocatalytic materials based on intramolecular and intermolecular D-A interactions, encompassing small molecules, conjugated polymers, crystalline polymers, supramolecules, and organic heterojunctions. Meanwhile, the energy band structures, exciton dynamics, and redox-active sites of D-A type organic photocatalytic materials under different bonding modes are discussed. Finally, the review highlights the advanced applications of organic photocatalystsand outlines prospective challenges and opportunities.

Keywords: D-A interactions; exciton dissociation; organic semiconductors; photocatalysis.

Figure 1

Schematic illustration of the differences between the three modification methods from the perspective of photocatalytic elementary processes. a) D‐A interactions. b) Interface engineering. c) Crystal engineering.

Figure 2

Molecular structure of thiophene and its derivatives with D‐A structure. a) The structure and microscopic images of the PCPyBDT molecule. Reproduced with permission.^{[ 58 ]} Copyright 2021, Royal Society of Chemistry. b) Four D‐A‐D conjugated molecular structures with different D and A units. c) Molecular structures with different numbers of thiophene units based on NDI acceptor.

Figure 3

Molecular structure of carbazole and derivatives with D‐A structure. a) The structure of the 2CzPN molecule. Reproduced with permission.^{[ 61 ]} Copyright 2019, Wiley‐VCH. b) Chemical and electronic structure of CNP molecule. c) Photocatalytic properties of different aggregation state structures. Reproduced with permission.^{[ 62 ]} Copyright 2023, Springer Nature. d) Molecular structures with different A units based on carbazole donors.

Figure 4

Molecular structures of diazole derivatives and other donor types with D‐A structures. a) Chemical and crystal structures of D‐A molecules based on imidazole and PDI. Reproduced with permission.^{[ 63 ]} Copyright 2023, Wiley‐VCH. b) Chemical structures of D‐A molecules containing different numbers of nitrogen atoms. c) Energy level structure of BDTD molecule based on triphenylamine donor. Reproduced with permission.^{[ 65 ]} Copyright 2019, Elsevier. d) Chemical structure of a triphenylamine‐PDI (D‐A) molecule with crystallinity. Reproduced with permission.^{[ 66 ]} Copyright 2022, Wiley‐VCH. e) Chemical structure of the SA‐TPP‐C₆₀ molecule. Reproduced with permission.^{[ 67 ]} Copyright 2022, Elsevier. f) Organic photovoltaic photocatalyst F1 molecules with D‐A units. Reproduced with permission.^{[ 68 ]} Copyright 2022, American Chemical Society.

Figure 5

D‐A conjugated polymers based on FSO acceptor. a) The chemical structure of FSO. b) Diagram of the synthetic routes of polymers PDBTSO‐T and PDBTSO‐2T. Reproduced with permission.^{[ 71 ]} Copyright 2022, Elsevier. c) The chemical structure of D‐A polymers with different cross‐linker lengths. Reproduced with permission.^{[ 72 ]} Copyright 2018, American Chemical Society. d) D‐A polymers based on thiophene units with different degrees of conjugation. Reproduced with permission.^{[ 73 ]} Copyright 2022, Royal Society of Chemistry. e) Schematic diagram of the principle that the sulphonyl group in FSO acts as an electron‐output “tentacle”. Reproduced with permission.^{[ 74 ]} Copyright 2019, Elsevier. f) The D‐π‐A polymer strategy with π‐bridge. Reproduced with permission.^{[ 75 ]} Copyright 2021, Wiley‐VCH.

Figure 6

D‐A conjugated polymers based on triazin acceptor. a) The chemical structure of triazine and its derivatives. b) Synthetic pathway toward sulfur and nitrogen‐containing porous polymers. Reproduced with permission.^{[ 80 ]} Copyright 2018, Wiley‐VCH. c) Chemical structure of carbazole‐triazine based CMPs. d) The mechanism of active oxygen generation. Reproduced with permission.^{[ 81 ]} Copyright 2018, Royal Society of Chemistry. e) The schematic for the preparation of D‐A polymers. f) The distribution of HOMO and LUMO wave functions of NMT400. g) Band gap of AMT400 and NMT400. Reproduced with permission.^{[ 82 ]} Copyright 2022, Wiley‐VCH.

Figure 7

D‐A conjugated polymers based on BT acceptor. a) The chemical structure of the BT molecule. b) Structures of polybenzothiadiazoles with different molecular designs. Reproduced with permission.^{[ 83 ]} Copyright 2016, Wiley‐VCH. c) The polymer molecules with D‐A and D‐π‐A structures. Reproduced with permission.^{[ 84 ]} Copyright 2018, Elsevier. d) Chemical structure of polymer dots. Reproduced with permission.^{[ 85 ]} Copyright 2017, Royal Society of Chemistry.

Figure 8

Imine‐linked D‐A type COFs with different structures. a) Bonding structure of Py‐XTP‐BT‐COFs based on BT acceptor. b) Monomers of the NKCOFs. c) Bonding structure of PyTz‐COFs based on Tz acceptor. d) The chemical backbones of the isomeric COFs based on triazine acceptor.

Figure 9

Full π‐conjugated D‐A type COFs with different structures. a) The structure with different geometrical symmetries based on vinylene‐linked COF. b) The structure of the Py‐BSZ‐COF. c) The structure of COF‐JLU35. d) The topology‐directed synthesis of the BDOV‐COFs with vinylene‐linked. e) The structure of triazine‐linked D‐A type COFs containing acetylene. f) The D‐A structured CTFs by sequential polymerization.

Figure 10

The D‐A type MOFs with different structures. a) Schematic diagrams for the construction of MOFs NS. b) Schematic diagram of the acceptor‐on‐donor NS. c) Schematic diagram of the donor‐on‐acceptor NS. Reproduced with permission.^{[ 109 ]} Copyright 2021, Wiley‐VCH. d) Crystal structure of JNU‐204. e) Schematic illustration of JNU‐204 as photocatalyst for aerobic oxygenation. Reproduced with permission.^{[ 110 ]} Copyright 2021, American Chemical Society. f) The structure and proposed photocatalytic reaction mechanism of D‐A type MOF Zr‐NDI‐H₂DPBP. Reproduced with permission.^{[ 111 ]} Copyright 2023, American Chemical Society.

Figure 11

Post‐modified strategy to construct D‐A type crystalline polymers. a) Schematic of converting open lattice into segregated D‐A COF. Reproduced with permission.^{[ 117 ]} Copyright 2014, American Chemical Society. b) Immobilization of C₆₀ within the pores of NU‐901. Reproduced with permission.^{[ 118 ]} Copyright 2023, Wiley‐VCH. c) Structure and absorption spectra of D‐A type MOF cocrystal. Reproduced with permission.^{[ 119 ]} Copyright 2023, Wiley‐VCH. d) Schematic representation of POM clusters by covalent binding in D‐A type COF. Reproduced with permission.^{[ 120 ]} Copyright 2022, American Chemical Society. e) The structure of monatomic Co‐modified D‐A type COFs, sp²c‐COF_dpy‐Co. Reproduced with permission.^{[ 121 ]} Copyright 2020, Elsevier.

Figure 12

The D‐A type two‐component supramolecules with different structures. a) The electrostatic potential distribution and molecular formula of TPPS, C₆₀‐NH₂, and TPPS/C₆₀‐NH₂. b) The UV–vis absorption spectroscopy of TPPS/C₆₀‐NH₂. c) The comparison of the hydrogen evolution rates of different materials. Reproduced with permission.^{[ 127 ]} Copyright 2021, Wiley‐VCH. d) The electrostatic potential distribution and molecular formula of PDI and TPPS. e) Scheme of charge transport route at the D‐A interface in TPPS/PDI. Reproduced with permission.^{[ 128 ]} Copyright 2022, Wiley‐VCH.

Figure 13

The D‐A type molecular cocrystal for photocatalysis. a) The common molecular stacking patterns in molecular cocrystals: Mixed or segregated stack. b) Diagram of large‐scale preparation and structure of molecular cocrystal. c) Schematic of the photocatalytic process in molecular cocrystal. d) Electron and hole transfer pathway based on the calculation of electronic coupling in cocrystal. Reproduced with permission.^{[ 130 ]} Copyright 2023, Royal Society of Chemistry.

Figure 14

The host‐guest materials for photocatalysis. a) Synthesis process and structure of the TBP⊂ExBox⁴⁺. Reproduced with permission.^{[ 135 ]} Copyright 2020, Wiley‐VCH. b) The mechanism of [4+2] cycloaddition in the presence of [2+2]_BTH‐F. Reproduced with permission.^{[ 136 ]} Copyright 2020, Wiley‐VCH. c) The mechanism and structure of the D‐A supramolecular complex. d) The mechanism for photocatalytic H₂ production by using DA[2]C⁴⁺. e) The mechanism for photocatalytic aerobic oxidation by using DA[2]C⁴⁺. Reproduced with permission.^{[ 137 ]} Copyright 2021, American Chemical Society.

Figure 15

The organic polymer heterojunction materials for photocatalysis. a) Chemical structures and energy levels of PTB7‐Th and EH‐IDTBR. Reproduced with permission.^{[ 28 ]} Copyright 2020, Springer Nature. b) Chemical structures of PM6, Y6, and PCBM (top), and schematic of exciton decay and electron transfer processes (bottom). Reproduced with permission.^{[ 138 ]} Copyright 2022, Springer Nature. c) Molecular structures of PFBT (D1), PFODTBT (D2), and ITIC. Reproduced with permission.^{[ 139 ]} Copyright 2021, American Chemical Society. d) Schematic of low structural disorder and trap density in 2D conjugated materials (top), and chemical structure of TPP. Reproduced with permission.^{[ 140 ]} Copyright 2021, Wiley‐VCH.

Figure 16

The D‐A type materials for photocatalysis hydrogen evolution. a) The photoreactor set‐up with reflective panel and FS‐TEG‐coated glass fibers. b) Diagram of FS‐TEG‐coated glass slides stacked in series. Reproduced with permission.^{[ 144 ]} Copyright 2020, Royal Society of Chemistry. c) Hydrogen‐gathering experiments of Py‐TP‐BTDO polymer under natural light. Reproduced with permission.^{[ 145 ]} Copyright 2023, American Chemical Society. d) Chemical structures of the S‐COF, FS‐COF, and TP‐COF photocatalysts. e) HR‐TEM image of FS‐COF. f) Photocatalytic hydrogen evolution performance of FS‐COF. Reproduced with permission.^{[ 146 ]} Copyright 2018, Springer Nature. g,h) Photocatalytic hydrogen evolution activities of CNP‐s and CNP‐f. i) Photocatalytic H₂O₂ production activities of CNP‐s and CNP‐f. Reproduced with permission.^{[ 62 ]} Copyright 2023, Springer Nature.

Figure 17

The D‐A type materials for photocatalysis H₂O₂ generation. a) Charge difference map of D‐A furan couple system, and schematic of H₂O₂ production mechanism. b) Scaled‐up photocatalytic system produced H₂O₂ continuously for 24 h. Reproduced with permission.^{[ 152 ]} Copyright 2023, Elsevier. c) The synthetic routes for the TA‐based polymer photocatalysts. Reproduced with permission.^{[ 153 ]} Copyright 2023, Wiley‐VCH. d) Schematic of the oxidation‐reduction molecular junction COF photocatalyst. Reproduced with permission.^{[ 154 ]} Copyright 2023, Wiley‐VCH. e) The chemical structure of Cu₃‐BT‐COF. f) Schematic of mechanism for H₂O₂ photosynthesis coupled with FAA photo‐oxidation by Cu₃‐BT‐COF. Reproduced with permission.^{[ 155 ]} Copyright 2023, Wiley‐VCH.

Figure 18

Electronic reactions and energy band structures involved in the photosynthesis of H₂O₂. a) The oxidation or reduction pathway for the photosynthesis of H₂O₂ from H₂O and O₂. b) Different redox pathways for photosynthesis H₂O₂ formation, and the corresponding redox potential. Reproduced with permission.^{[ 158 ]} Copyright 2020, Royal Society of Chemistry.

Figure 19

The D‐A type materials for photocatalysis CO₂ reduction. a) Schematic for the structure and synthesis of TPA‐PQ. b) Catalytic cycle with the different intermediates. Reproduced with permission.^{[ 160 ]} Copyright 2021, American Chemical Society. c) Electron transfer and reaction pathway in CT‐COF for the photoreduction of CO₂. Reproduced with permission.^{[ 161 ]} Copyright 2020, Wiley‐VCH. d) The mechanism of sp²c‐COF_dpy‐Co for CO₂ photoreduction reaction. Reproduced with permission.^{[ 121 ]} Copyright 2020, Elsevier. e) The mechanism of TCOF‐MnMo₆ for H₂O oxidation and CO₂RR. f) Free energy for H₂O oxidation in TCOF‐MnMo₆. Reproduced with permission.^{[ 120 ]} Copyright 2022, American Chemical Society.

Figure 20

The D‐A type materials for environmental photocatalysis. a) Photocatalytic phenol degradation performance of PDI derivatives. Reproduced with permission.^{[ 63 ]} Copyright 2023, Wiley‐VCH. b) The structure and electrostatic potential distribution of PCN‐5B2T. Reproduced with permission.^{[ 166 ]} Copyright 2023, American Chemical Society. c) Chemical and electronic structure of COF‐TD1. d) Photocatalytic degradation performance of COF‐TD1 in a scale‐up reactor under natural sunlight irradiation. Reproduced with permission.^{[ 167 ]} Copyright 2022, American Chemical Society. e) The diagram of the photocatalytic sterilization mechanism of P7/g‐C₃N₄. f) SEM images of E. coli before and after treatment with P7/g‐C₃N₄. Reproduced with permission.^{[ 168 ]} Copyright 2022, Elsevier.

Figure 21

The D‐A type materials for organic transformations. a) The structure of TA‐Por‐sp²‐COF, and the reaction path of the benzylamine coupling. Reproduced with permission.^{[ 169 ]} Copyright 2022, American Chemical Society. b) Photocatalytic mechanisms of Py‐BSZ‐COF‐mediated oxidative amine coupling. Reproduced with permission.^{[ 103 ]} Copyright 2020, American Chemical Society. c) The energy level of the dBIP molecule with two‐photon absorption properties. d) Photocatalytic performance of dBIP under infrared irradiation. Reproduced with permission.^{[ 170 ]} Copyright 2023, American Chemical Society. e) The structure of D‐A type COF OH‐TFP‐TTA, and schematic energy band structure with different compositions. f) The photo‐reductive dehalogenation reactions over OH‐TFP‐TTA. Reproduced with permission.^{[ 171 ]} Copyright 2020, American Chemical Society. g) The crystal structure and pictures of crystals of m‐TPE Di‐EtP5⊃G2. Reproduced with permission.^{[ 172 ]} Copyright 2023, Wiley‐VCH.