Illuminating innovations: design and synthesis of maleimide fluorophores inspired by luminescence mechanisms and structural characteristics

Lu, Yu (2025). Illuminating innovations: design and synthesis of maleimide fluorophores inspired by luminescence mechanisms and structural characteristics. University of Birmingham. Ph.D.

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Abstract

Maleimide-type fluorophores have attracted significant attention over the years due to their various advantages. For instance, maleimide molecules are relatively small and possess multiple modification sites, facilitating the synthesis of fluorophores with different emission wavelengths. Additionally, the push-pull system and twisted intramolecular charge transfer emission mechanism endows maleimide-type fluorophores with features such as solvatochromism and sensitivity to microenvironmental changes. Therefore, based on the structural and luminescent characteristics of maleimide molecules, the main work of this thesis involves designing and synthesising different types of fluorescent compounds.
Dual state emission molecules represent a novel class of fluorophores that possess efficient luminescence capabilities in both solution and aggregated states. They hold great potential for applications in various fields such as bioimaging and information anti-counterfeiting. The work in Chapter 2 demonstrates a series of maleimide derivatives with dual-state emission properties. By attaching para-haloanilines and 4-n-butylaniline to the nitrogen atom of the imide ring and the double bond site, respectively, efficient luminescence in both solution and solid states was achieved (with quantum yields up to 41.9% in solution and 84.1% in the solid state). Further single-crystal structure analysis revealed the effect of substituent positions on the intramolecular torsion angles. Finally, theoretical calculations validated the experimental results and provided in-depth insights into the molecular luminescence mechanism. This study presents a universal design strategy for dual-state emission molecules, paving the way for the development of next-generation fluorescent materials.
The work in Chapter 3 demonstrates a series of maleimide derivatives with photochromic properties. Aiming at the research gap in functionalized maleimide derivatives, a strategy was proposed to prepare a series of fluorophores exhibiting photochromism via photoisomerization and photocycloaddition by attaching photoresponsive groups to the nitrogen atom site of the imide ring. First, fluorescence spectroscopic characterization of azobenzene-based maleimide molecules revealed their photochromic properties, followed by theoretical calculations to explore the photochromic mechanism. Furthermore, the successful photochromism achieved by connecting different photoresponsive groups to maleimide validated the universality of this molecular design strategy. This study presents a novel and simple design concept for photochromic molecules, contributing to the further development of photoresponsive materials.
The work in Chapter 4 investigates the room-temperature phosphorescence (RTP) properties of maleimide derivatives. In view of the absence of research reports on the RTP properties of maleimide molecules, this study first proposes the realization of RTP through a host-guest doping strategy. Initially, RTP characterization using benzophenone and 4-phenylmaleimide as small-molecule hosts failed to observe RTP; subsequently, RTP was achieved using PMMA polymer as the host. Theoretical calculations were further conducted to explore the phosphorescence mechanism of such molecules. This study demonstrates the potential of maleimide derivatives to achieve RTP, providing more molecular design options for the development of the room-temperature phosphorescence field.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):