Synthesis and application of a thienoisoindigo-based acceptor small molecule for organic photodetectors

Abstract

Small molecules with an acceptor–donor–acceptor (A–D–A) structure, exhibiting strong intramolecular charge transfer effects and adjustable energy levels, contribute to broadening the spectral response range and enhancing the specific detectivity (D*) of organic photodetectors (OPDs). In this study, a narrow-bandgap organic small-molecule acceptor, TIIG-T-EM, with an A–D–A′–D–A architecture was designed and synthesized. The molecule features thienoisoindigo (A′) as the central building block, thiophene (D) as the π-bridge, and 2-(3-ethyl-4-oxo-thiazolidin-2-ylidene)-malononitrile as the electron-withdrawing end groups (A). Its thermal stability, optical properties, electrochemical characteristics, and device performance were systematically investigated. The results indicate that TIIG-T-EM exhibits good solubility and thermal stability, with an optical bandgap of 1.32 eV and strong absorption in the 300–1000 nm range, achieving a molar extinction coefficient of 121 880 L mol⁻¹ cm⁻¹. OPDs fabricated using PBDB-T as the donor material demonstrated a maximum D* of 8.19 × 10¹¹ Jones at 450 nm and 1.93 × 10¹¹ Jones at 800 nm, underscoring the potential of this molecule for applications in OPDs.