Boron and Nitrogen (BN) Doped Helicenes with High Performance Circularly Polarized Luminescence: New Materials Synthesis, Fundamental Mechanism, and Devices Engineering.

Professor Liu, Junzhi   (Project Coordinator (PC))

Professor Chow Chi Yung Philip   (Co-principal investigator)

Professor Che Chi Ming   (Collaborator)

12

2025-06-01

1666000

Boron and Nitrogen (BN) Doped Helicenes with High Performance Circularly Polarized Luminescence: New Materials Synthesis, Fundamental Mechanism, and Devices Engineering.

""1) Helicenes"", ""2) Boron and nitrogen atoms"", ""3) Polycyclic aromatics"", ""4) Polarized luminescence"", ""5) OLEDs""

Chemical Sciences

Physical Sciences (P)

C7004-24Y

Collaborative Research Fund (CRF) - Group Research Project 2024/2025

2024

On-going

Objective 1: Design and Synthesis of New Chiral Molecular Materials  1) BN-doped single-stranded helicenes. The current state of the art utilizes axially or helically chiral molecules with donor-acceptor structures as the chiral emitters. The BN-doped emitters with helicene structures have not been well developed. In this objective, we will synthesize a series of BN-doped single-stranded helicenes (Figs. 2a-2c), which feature different chirality to tune the optical and electronic properties. In addition, by comparing with their corresponding pristine carbohelicenes, we also can figure out the advantages by introducing BN units into the helicenes in this objective. 2) π-Extended and multiple helicenes with BN units. From our preliminary results, we found that the incorporation of BN atoms into the framework of helicenes can improve the CPL performance of carbohelicenes. For instance, the maximum gabs of BN-[6]helicene is 0.021, an order of magnitude larger than pure carbon [6]helicene (10-3) (Fig. 9c). In this objective, π-extended helicenes with double NBN units will be explored (Fig. 2e), to investigate the number of BN units to affect the chiroptical properties, and further improve the CPL performance (e.g., achieve large glum values). 3) Inner BN-doped π-expanded helicenes: benzo-extended heli(iminoborane)s (HIBs). Generally, incorporation of main group elements is an effective strategy to improve novel chiral photophysical properties. Another promising method of enhancing helicity and tuning the chiroptical properties is ""spine surgery"" of highly twisted backbones (Fig. 3a). However, the inner BN-doped π-expanded helicenes have not been successfully achieved yet. In this objective, we will develop the chiral emitters with different topologies, in which the BN atoms will be introduced into the inner framework, namely benzo-extended heli(iminoborane)s (Fig. 3). We will further address the trends in the electronic, chiroptical properties and the performance of the CP-OLED devices caused by increasing the number of BN units. Objective 2: Understanding of the Fundamental Mechanism. Despite already achieving high CPL performance, the fundamental electronic properties and circularly polarized light emission mechanism for these BN-doped helicenes have remained unclear, hindering rational material development and performance optimization. In this objective, we target to combine experimental and theoretical studies to establish a comprehensive understanding of structure-property relationship of these novel chiral molecules. Specifically, we target to perform timeresolved optical spectroscopy measurements to reveal the excited state dynamics. By optically probing with ultrafast temporal resolution (i.e. using pump-probe experiments), we will obtain detailed understanding of the exciton and chargetransfer (CT) properties in the BN-helicenes and their aggregates. Temperature dependent measurements will be performed to study the precise mechanism of light emission (fluorescence, phosphorescence or CT-mediated thermally activated delayed fluorescence (TADF)). Furthermore, polarization-dependent measurements will be used to reveal the chiral properties of excitons. Quantum-chemical calculations including density functional theory and molecular dynamics simulations will be performed to determine energy levels, electron wavefunction distributions, oscillator strength, electronic and vibrational couplings of the BNdoped helicenes.  Objective 3: Devices Engineering To establish clear structure-property relationships for the application of BN-doped helicenes, such as the number of BN units and chirality, etc. The relevant CP-OLED devices will be fabricated based on the synthesized BN-doped chiral materials (through collaborations with our partner Co-I Prof. Chi-Ming Che, please see the attached support letter). As the key achievements, we expect to establish a novel solution-based materials chemistry, delineation of reliable structure-property relationships and superior device performance of BN-helicenes for CP-OLEDs.