Doctor of Philosophy (Ph.D.)
Degree Granting Department
Xiaopeng Li, Ph.D.
Jianfeng Cai, Ph.D.
Shengqian Ma, Ph.D.
Jing Wang, Ph.D.
Phosphorescent, Self-Assembly, Terpyridine
Pyrylium salts are a type of six-membered cationic heterocycles with one positively charged oxygen atom. Since the discovery of pyrylium salts in 1911, such salts have been underappreciated for a long time. Until 1960s, the importance of pyrylium salts has been realized as versatile precursors in a variety of organic syntheses. Due to their high reactivity towards various nucleophiles, pyrylium salts were widely used for the convenient synthesis of diverse heterocyclic compounds. Starting from 1980s, the high reactive feature of pyrylium salts were further utilized to synthesize viologen polymers with pyridinium salts in the backbones. During the past two decades, pyrylium salts have been employed by Höger and Müllen as a powerful toolbox for the preparation of discrete organic macrocycles with well-defined sizes, shapes and structures. More recently, Li and coworkers have further employed pyrylium salts to prepare multitopic pyridinium salts building blocks for the construction of discrete metallo-supramolecules based on coordination-driven self-assembly. However, most of these discrete organic and metallo-organic constructs were limited to two-dimensional (2D) architectures without functional groups. Moreover, three-dimensional (3D) structures are still rare based on pyrylium salts chemistry.
In this dissertation, a giant but discrete metallo-supramolecular concentric hexagon (S) was designed and functionalized with six Pt(II) bzimpy (bzimpy=2,6-bis(benzimidazole-2’-yl) pyridine) motifs based on pyrylium salt chemistry. In the design, a terminal alkynyl group was employed to install the Pt(II) motif with a stable and rigid Pt(II)-alkynyl bond for further self-assembly. Also, multiple hydrophilic ethylene glycol chains were introduced into bzimpy moieties on the periphery, and long alkyl chain (C12) was decorated in the interior to tune the aggregation through balancing the overall hydrophobicity/hydrophilicity. With a size larger than 10 nm and a molecular weight higher than 26,000 Da, the assembled terpyridine (tpy)-based supramolecule containing six Pt(II) centers displayed phosphorescent emission with a lifetime of 218 ns at room temperature. By synergistically combining aggregation-induced phosphorescent emission (AIPE) from Pt(II) luminophores and aggregation-induced emission (AIE) features from Cd(II)-tpy assemblies, the functionalized supramolecule S exhibited significantly enhanced AIPE compared to the ligand L. Via tuning the aggregation states of the functionalized ligand L and S, their AIPE behaviors were carefully investigated. More interestingly, further enhancement of phosphorescent emission was observed in both L and S when purged by CO2 gas.
Beyond 2D architectures, a giant tetrahedron cage with four concentric hexagons as faces was successfully achieved through coordination-driven self-assembly of octatopic tpy building block based on pyrylium salts chemistry. Instead of synthesizing the entire face prior to the self-assembly, the faces with concentric hexagons were constructed along with the coordination process. Individual face units were connected by organic linker with specific angles to control the geometry of the final structure. In the entire 3D architecture, organic ligands served as vertices and parts of the faces, metal ions were used to bridge the building blocks for the formation of the faces. The formation of the tetrahedron cage was confirmed by electrospray ionization-mass spectrometry (ESI-MS) and traveling wave ion mobility-mass spectrometry (TWIM-MS). In addition, the structure was clearly observed by TEM with corresponding shape and size. This novel design and synthesis strategy allowed us to construct giant 3D supramolecular architectures with increasing size and complexity, and will advance further study for potential applications such as protein encapsulation, large biomolecule transportation and so on.
Scholar Commons Citation
Li, Yiming, "Construction of Giant 2D and 3D Metallo-Supramolecules Based on Pyrylium Salts Chemistry" (2020). USF Tampa Graduate Theses and Dissertations.