| Author: | Wong, Ho Chun |
| Title: | Non-conjugated photoluminescent polymer particles: synthesis, characterization and potential application |
| Advisors: | Li, Pei (ABCT) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Department: | Department of Applied Biology and Chemical Technology |
| Pages: | xvi, 208 pages : color illustrations |
| Language: | English |
| Abstract: | Fluorescent materials are important for their potential applications in a wide range of applications. However, conventional conjugated organic dyes are non-fluorescent in the aggregated or solid state, which limits their practical applications. This decrease in fluorescence intensity is caused by the π-π stacking induced by molecular aggregation. In the past decade, there is increasing research efforts to develop next generation of non-conjugated fluorescence materials with strong emission in the aggregated (nanoparticle) and solid-state through restricting intramolecular motion. The first chapter provides an overview of current fluorescent materials, including traditional dyes, fluorescent proteins, conjugated polymer, polymer-based nano-dots, and quantum dots. Their distinctive properties, photoluminescence mechanisms, and existing limitations are discussed. This chapter also introduces a novel type of fluorescent material called nonconjugated fluorescence polymeric (NCFP) particles including their characteristics, synthesis methods, mechanisms, optical properties, and potential applications. The second chapter provides the rationale and objectives of the research, which aims to the development of non-conjugated fluorescence polymeric particles with high emission in aqueous, while also exploring their potential applications. Two distinct approaches for preparing the NCFP particles have been developed. The first approach involves crosslinking polyethyleneimine (PEI) with glutaraldehyde (GA), followed by a graft co-polymerization of an acrylic-based monomer onto the PEI to generate zwitterionic nanoparticles. The second approach involves the post-treatment of PEI-based core-shell particles through crosslinking of the hydrophilic shell to generate nano-dots using small molecules containing two or three carboxylic acid groups. The third chapter describes the synthesis, characterization and application of NCFP particles in nano size with strong green fluorescence. The nanoparticles were synthesized through the crosslinking PEI with glutaraldehyde (GA), followed by a graft co-polymerization of an acrylic acid-based monomer onto the PEI to form zwitterionic complexed nanoparticles. This approach was designed to create the effect of crosslink enhancement emission (CEE), specifically covalent-bonding CEE and ionic-bonding CEE. By optimizing the degree of crosslinking, reaction conditions as well as structure of monomer and monomer ratios of the graft-copolymerization reaction, the glutaraldehyde-crosslinked PEI/poly(methylacrylic acid) (gPEI/PMAA) nanoparticles possess the best performance characterized by their high size monodispersity with an average diameter of 34.6 nm, excitation–dependent fluorescence with the maximum green emission at 527 nm under excitation of 480 nm, and high quantum yield of up to 23.6% when compared to Rhodamine 6G as a standard. The potential application in LED light was demonstrated by embedding the dried gPEI/PMAA nanoparticles in the silicon and coating it onto a monochromic blue light emitting diodes (LED) chip. The light parameters, including correlated color temperature (CCT), color rendering index (CRI), and deep ultraviolet (Duv) of the NCFP nanoparticle-coated LED chip were analyzed, and results indicated that the LED chip could produce white to warm light LED in the nature. This simple fabrication method will highly simplify the production of LED light which required a combination of two to third photophores. The fourth chapter of this thesis describes another approach to prepare fluorescent latexes based on PEI-based amphiphilic core-shell particles. A series of experiments were conducted to crosslink the PEI shell of the PEI/poly(methyl methacrylate) (PEI/PMMA) particles using crosslinkers bearing two or three carboxylic acid groups. Notably, the modification of the particles with citric acid (CA) yielded the highest fluorescence intensity. The latexes and the isolated fluorescent solution were subjected to characterization, which indicated the formation of carbon dots (CDs) embedded on the surface of the non-fluorescence particles. Importantly, this was achieved without resorting to the conventional methods of hydrothermal or microwave irradiation. Further optimization experiments were undertaken, focusing on variables such as the molecular weight of PEI, the core-to-shell ratio of the particles, and the composition of the core. Ultimately, water-dispersible CA-modified PEI/poly(methyl methacrylate-co-butyl acrylate) [PEI/P(MMA-co-BA)] particles were successfully synthesized, and possessed uniform particle size with average particles diameter of 193 nm and high fluorescence emission at 440 nm when excited by 360 nm. In conclusion, the research conducted in this thesis has provided insights into the development of non-conjugated fluorescence polymeric materials, showcasing their potential for LED light and energy saving. The findings presented here lay the foundation for further investigations to achieve tunable fluorescent properties with high quantum yield, thereby enabling a broader range of photoluminescence properties. Moreover, future studies should focus on the exploration of these materials' potential in areas such as sensing, imaging, and optoelectronics, thus contributing to the advancement of fluorescent material technology. This research will also open up new pathway for the future designs and synthesis of highly efficient and versatile non-conjugated fluorescent materials, propelling the field towards new frontiers of scientific and technological innovation. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/14556