Synthesis and characterization of a large Stokes-shifted fluorescent imide and its related polyimides bearing 2-(2′-hydroxyphenyl)benzothiazole moieties†
Abstract
A large Stokes-shifted fluorescent imide (HBTN-MC) and its related polyimides (HBHBTNms and HPHBTNms) were first designed and synthesized by introducing an excited state intramolecular proton transfer fluorophore 2-(2′-hydroxyphenyl)benzothiazole (HBT). The imide exhibited a large Stokes shift of 9654 cm−1 in the dichloromethane solution and 7648 cm−1 in the solid state. Based on the experimental and theoretical methods, the photophysical properties and the excited state intramolecular proton transfer (ESIPT) process of HBTN-MC have been systematically studied. The performances of the polyimides have been optimized by changing the alicyclic dianhydride and adjusting the copolymerization ratio. The as-prepared polyimide films retained the ESIPT performance with a large Stokes shift of larger than 8105 cm−1, a high photoluminescence quantum efficiency (φ) of 29%, decent colorless and transparency, high thermal performance (Td, 5% = 468 °C and Tg > 260 °C), and solubility in both conventional aprotic and protic solvents. In short, the newly developed imide and polyimides provide good examples for the development of ESIPT polymers with controllable emission wavelengths as well as high thermal, environmental, and radiation stability.