Abstract
Polymers of intrinsic microporosity (PIMs) are organic porous materials that normally have high specific surface areas (e.g. 720-875 m2 g-1 for typical PIM-1) and microporous pores (pore size < 2 nm). The high surface area, solution processability, excellent molecular separation performance, and good thermal stability give PIMs broad application prospects, especially in gas separation, storage, water purification, and heterogeneous catalysis. This study pioneered the incorporation of PIMs into optoelectronic applications, especially light harvesting applications, transforming their traditional role as gas-selective materials into high-performance components of luminescent solar concentrators (LSCs).By introducing the unique spirocyclic structure of PIM-1 and its derivatives, a series of PIMs with tuneable optical properties was designed. The initial LSC prototype, fabricated with a thin film of PIM-1 and a fluorescent dye (LR305) on a high-refractive-index glass substrate and a size of 5 × 5 cm, displayed high edge-emission efficiency (71 % of emitted light concentrated to the edges) and competitive optical efficiencies (25.3 % and 12.6 % for internal and external optical efficiencies, respectively).
A computational study carried out on dimer models of PIMs revealed that the orthogonal geometry of the spiro-linked segments enables degenerate frontier orbitals (ΔE ≈ 0.02 eV) and splitting in the excitation transition, revealing the existence of spiroconjugation in PIMs with spiro-centric structures. These phenomena have been proven by experimental measurements, including optical spectra and fluorescence quenching.
Inspired by the molecular orbitals study, several modified PIMs were synthesised and characterised, and additional LSC prototypes based on modified PIMs and LR305 were made and analysed. Their maximum external efficiency of 6.5% demonstrates the potential of well-designed PIMs as light-harvesting antennas for LSC devices. It also validates the use of the computational model to design PIM-1-like polymers with specific optoelectronic requirements.
Finally, in an effort to enhance scalability, luminophores were doped into poly(methyl methacrylate) and styrene-ethylene-butylene-styrene polymer substrates rather than spin-coating them on glass surfaces. Increasing the concentrations of luminophores led to enhanced photoluminescent quantum yield, attributed to improved Forster Resonance Energy Transfer efficiencies with reduced interchromophore distances. By doping 10,000 ppm of PIM-1 and 100 ppm of LR305 into a PMMA substrate, the internal and external photon efficiencies can reach up to 20.6 % and 19.2 %, respectively, which highlights the potential of this material combination for window-type LSC applications.
In summary, this research repositions the type of microporous polymers known as “polymers of intrinsic microporosity” as multifunctional materials for sustainable energy technologies, offering transformative potential for solar windows, photocatalytic membranes, and other optoelectronic applications.
| Date of Award | 17 Jun 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Charl F J Faul (Supervisor) & Sebastien Rochat (Supervisor) |