Substituent groups effects on AIEgens of fluorenone derivatives: Optical properties, bioimaging, and LED devices

Abstract

Understanding structure-property relationships is crucial for developing materials with a high fluorescence quantum yield (Φ_F) and optimizing their performance. In this study, three fluorenone-carbazole-based molecules (FO-Cz1, FO-Cz2, and FO-Cz3) were synthesized, which have similar structures but varying substituent groups (carbazole, 3,6-di‑tert‑butyl‑9H-carbazole, and 3,6-diphenyl-9H-carbazole). The different substituent groups significantly changed the optical properties of the luminogens. The experimental results confirmed that FO-Cz1, FO-Cz2, and FO-Cz3 were AIEgens, and the introduction of a phenyl group gave FO-Cz3 strong α_AIE (I/I₀) and greater solid fluorescence quantum yields than FO-Cz1 and FO-Cz2. Analysis of photophysical properties, theoretical calculations, and X-ray crystallography revealed that the emission properties of FO-Cz1, FO-Cz2, and FO-Cz3 were influenced by the use of flexible substituent groups. The substituent groups avoided π-π stacking, reduced non-radiative transitions, and enhanced fluorescence in the aggregated state. Substituent groups on the benzene ring gave FO-Cz3 a tightly-packed structure and strong emission. It was used for cancer cell imaging and LED devices, in which FO-Cz3 exhibited high photostability and biocompatibility, making it a superior photosensitizer for bioimaging and applications in OLED devices. This research sheds light on the AIE behaviors of fluorenone complexes and offers valuable insights for the development of organic luminescent materials.