Low Bandgap Donor-Acceptor π-Conjugated Polymers From Diarylcyclopentadienone-Fused Naphthalimides

Abstract

Two novel aromatic imides, diarylcyclopentadienone-fused naphthalimides (BCPONI-2Br and TCPONI-2Br), are designed and synthesized by condensation coupling cyclopentadienone derivatives at the lateral position of naphthalimide skeleton. It has been found that BCPONI-2Br and TCPONI-2Br are highly electron-withdrawing acceptor moieties, which possess broad absorption bands and very low-lying LUMO energy levels, as low as −4.02 eV. On the basis of both building blocks, six low bandgap D-A copolymers (P1–P6) are prepared via Suzuki or Stille coupling reactions. The optical and electrochemical properties of the polymers are fine-tuned by the variations of donors (carbazole, benzodithiophene, and dithienopyrrole) and π-conjugation linkers (thiophene and benzene). All polymers exhibit several attractive photophysical and electrochemical properties, i.e., broad near-infrared (NIR) absorption, deep-lying LUMO levels (between −3.88 and −3.76 eV), and a very small optical bandgap as low as 0.81 eV, which represents the first aromatic diimide-based polymer with an of <1.0 eV. An investigation of charge carrier transport properties shows that P5 exhibits a moderately high hole mobility of 0.02 cm 2 V −1 s −1 in bottom-gate field-effect transistors (FETs) and a typical ambipolar transport behavior in top-gate FETs. The findings suggest that BCPONI-2Br, TCPONI-2Br, and the other similar acceptor units are promising building blocks for novel organic semiconductors with outstanding NIR activity, high electron affinity, and low bandgap, which can be extended to various next-generation optoelectronic devices.

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“…This reduction in the energy gap is ascribed to the influence of the density of localized states and is preferred for solar energy applications (Ahmed and Abdalla, 2020;Helmy et al, 2020;Mohamed et al, 2020;Shaban and El Sayed, 2020;. This behavior is consistent with the previously reported studies (Li et al, 2019). The strong absorption in the Visible/IR region and the extension of the bandgap edges are very important for solar energy applications, especially photoelectrochemical hydrogen generation and solar cells (Abdelmoneim et al, 2021;Mohamed et al, 2021;Shaban et al, 2021).…”

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“…This behavior is consistent with the previously reported studies. 79 The strong absorption and the extension of the bandgap edges are very important for solar energy applications, especially photoelectrochemical hydrogen generation, and solar cells. 80–82 …”

“…This behavior is consistent with the previously reported studies. 79 The strong absorption and the extension of the bandgap edges are very important for solar energy applications, especially photoelectrochemical hydrogen generation, and solar cells. [80][81][82] Urbach energy (E U ) refers to the disorder in the material and represents the width of the exponential absorption edge (Urbach tail of the valence and conduction bands).…”

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