(4j) Hierarchical Molecular Design at the Organic-Inorganic Interfaces and Photonics Applications

Research Interests: My research focuses on designing organic building blocks for purely organic and organic-inorganic hybrid semiconductors. The design transfers molecular orbit manipulation and molecular-level interactions to the structures and morphologies, and ultimately the photonic and electronic properties of the self-assembled systems.

Keywords: First Principles Molecular Design; Organic-Inorganic Hybrid Semiconductors; Layered Materials; Photonics; Light-Emitting Devices.

Abstract:

Designing organic building blocks and understanding their structure-functional relationships are crucial in modern electronic, photonic, and bio-integrated systems due to their low-cost fabrication and vast chemical space. The increasing design complexity from purely organic materials to hybrid crystals and interfaces necessitates a solid connection between structures, molecular orbital manipulation, self-assembly, electronic, and luminescent properties. Given the virtually infinite molecular space, navigating through it to find candidates with the optimum functionality is extremely challenging. However, this is different in organic-inorganic hybrid materials. The defined lattice parameters converge molecular-level structural and electronic manipulation with "macroscopic" morphological and photonic properties in a highly predictable and designable fashion. In this talk, I hope to introduce the hierarchical material design of hybrid materials as one of the core concepts to be explored in my independent career.

A representative approach I introduced to layered materials is called "topological modification". In our first report, an 1D organic network was created in layered perovskites using robust and directional hydrogen bonding from aromatic carboxylic acids. This molecular templating method restricted the crystal growth along all directions except for a designed primary axis and promoted 1D growth (1). Our approach is widely applicable to synthesize a range of high-quality layered perovskite nanowires with large aspect ratios and tunable chemical compositions, including the deterministic synthesis of longitudinal heterostructures. These nanowires form exceptionally well-defined and flexible cavities that exhibited a wide range of unusual optical properties beyond those of conventional perovskite nanowires. We observed anisotropic emission polarization, low-loss waveguiding and efficient low-threshold light amplification.

The chemistry of hybrid crystals can be seen as exploiting molecular chemistry in a confined inorganic lattice. Topological modifications emphasized this concept by imprinting molecular-level interactions to macroscopic morphology in a highly predictable fashion, and such simple but magical behavior finds origin in the unique self-assembled hybrid lattice. In the second part of the talk, I will push forward to hierarchical material design concept to explore hybrid materials and their chemical and photonic applications in a unconventional fashion. Two representative topics will be discussed:
1) The asymmetric strain built in such an 1D network topology can be explored to create a primary bending axis in layered materials to allow for the automatic generation of morphological chirality during crystal growth. I will argue that helicoids or helical ribbons can be synthesis in a scalable fashion out of layered materials with no structural acentrosymmetric centers. These new morphologies can helps us manipulate light-matter interactions and nonreciprocal transport in chiral micro- and nano-photonics.
2) In hybrid materials, the inorganic lattice can carry catalytic characteristics. This, along with their defined lattice parameters, allows unconventional organic reactions "on surface" in an "ordered lattice", which finds resonance with the on-surface organic synthesis but in an scalable manner. A system proposed in this criteria is the in situ polymerization of the organic lattice for the deterministic synthesis of 1D and 2D polymers.

Reference: (1) Shao, W., et al. Science, 2024, 384(6669), 1000–1006. https://doi.org//10.1126/science.adl0920

Teaching Interests: Organic chemistry; Solid-state chemistry; Organic semiconductors; Molecular photochemistry.

My teaching philosophy begins with two fundamental principles: From the perspective of the student, teaching is about facilitating "learning" — not only acquiring the expertise and mindset essential to their discipline, but also cultivating personal growth and character development. From the perspective of knowledge, teaching is a means to "pass on" expertise, to disseminate and share it across disciplines, ensuring its continual enrichment and transmission from one generation to the next.