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. 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.