Constructing red and near-infrared AIEgens for OLEDs and bioimaging

Abstract

Aggregation-induced emission luminogens (AIEgens), as the new kind of organic emitting materials, are dim or non-emissive in the solution/single molecule state, while emit intensively in the aggregated/solid state. This characteristic is contradictory to the traditional luminopohores and become the excellent method to deal with aggregation-caused quenching (ACQ) problem in the real applications, such as biological areas and optoelectronic devices. Efforts have been dedicated to study the mechanisms of AIE and different theories have been brought about to guide the design of new materials. Meanwhile, more attentions have paid to aggregate state to study the relationship between structures and properties, instead of just focus on the single molecule. Luminophores with long emission wavelength have always suffered from the low quantum efficiency and complicated synthesis, which hindered their applications. In this thesis, my work mainly focuses on constructing new red and near infrared (NIR) AIEgens, and developing their potential applications in organic light-emitting diodes (OLEDs) and bioimaging. Donor–accepter (D–A) system with charge transfer is commonly utilized to develop red and NIR luminescent materials. Start from following and improving previous work, two D–A–D’ red AIEgens have been synthesized and studied, which showed high quantum efficiency and good results in the simple nondoped OLEDs device. Then, a series of D–A–A structured molecules with different fluorine (F) substituents have been developed and compared to find out the relationship between structures and photophysical properties affected by different intra/intermolecular interactions. Solution processing method has been selected to further simplify the OLED process, and they exhibited fair performance in the nondoped devices. To further increase the emission wavelength to NIR region, a new acceptor core has been constructed and employed to form new AIEgens. The resulted molecules successfully extended the emission peak to 800–900 nm with high quantum yield. When applied to solution processed OLEDs, both the doped and nondoped devices showed top performances. Except for the optoelectronic devices, one newly developed asymmetric red AIEgen could be utilized for droplet lipid imaging in all levels of bio-substances, including live cells, tissues and live embryos with high specificity. Meanwhile, it has a large two-photon absorption cross-section to yield two-photon imaging with high resolution.

Date of Award	2021
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Benzhong TANG (Supervisor)