A Comparative Photophysical Study of Structural Modifications of Thioflavin T-Inspired Fluorophores.

The benzothiazolium salt, Thioflavin T (ThT), has been widely adopted as the "gold-standard" fluorescent reporter of amyloid in vitro. Its properties as a molecular rotor result in a large-scale (∼1000-fold) fluorescence turn-on upon binding to β-sheets in amyloidogenic proteins. However, the complex photophysics of ThT combined with the intricate and varied nature of the amyloid binding motif means these interactions are poorly understood. To study this important class of fluorophores, we present a detailed photophysical characterization and comparison of a novel library of 12 ThT-inspired fluorescent probes for amyloid protein (PAPs), where both the charge and donor capacity of the heterocyclic and aminobenzene components have been interrogated, respectively. This enables direct photophysical juxtaposition of two structural groups: the neutral "PAP" (class 1) and the charged "mPAP" fluorophores (class 2). We quantify binding and optical properties at both the bulk and single-aggregate levels with some derivatives showing higher aggregate affinity and brightness than ThT. Finally, we demonstrate their abilities to perform super-resolution imaging of α-synuclein fibrils with localization precisions of ∼16 nm. The properties of the derivatives provide new insights into the relationship between chemical structure and function of benzothiazole probes.EPSRC Follow on Fund, EPSRC DTC, Royal Society UR

Luminescent Solar Concentrators Based on Energy Transfer from an Aggregation-Induced Emitter Conjugated Polymer.

Luminescent solar concentrators (LSCs) are solar-harvesting devices fabricated from a transparent waveguide that is doped or coated with lumophores. Despite their potential for architectural integration, the optical efficiency of LSCs is often limited by incomplete harvesting of solar radiation and aggregation-caused quenching (ACQ) of lumophores in the solid state. Here, we demonstrate a multilumophore LSC design that circumvents these challenges through a combination of nonradiative Förster resonance energy transfer (FRET) and aggregation-induced emission (AIE). The LSC incorporates a green-emitting poly(tetraphenylethylene), p-O-TPE, as an energy donor and a red-emitting perylene bisimide molecular dye (PDI-Sil) as the energy acceptor, within an organic-inorganic hybrid diureasil waveguide. Steady-state photoluminescence studies demonstrate the diureasil host induced AIE from the p-O-PTE donor polymer, leading to a high photoluminescence quantum yield (PLQY) of ∼45% and a large Stokes shift of ∼150 nm. Covalent grafting of the PDI-Sil acceptor to the siliceous domains of the diureasil waveguide also inhibits nonradiative losses by preventing molecular aggregation. Due to the excellent spectral overlap, FRET was shown to occur from p-O-TPE to PDI-Sil, which increased with acceptor concentration. As a result, the final LSC (4.5 cm × 4.5 cm × 0.3 cm) with an optimized donor-acceptor ratio (1:1 by wt %) exhibited an internal photon efficiency of 20%, demonstrating a viable design for LSCs utilizing an AIE-based FRET approach to improve the solar-harvesting performance

Design of high-performance luminescent solar concentrators based on aggregation-induced emitters in organic-inorganic hybrid waveguides

Solar-harvesting systems that have the potential to be integrated into the urban built environment have attracted significant interest. However, traditional solar panels are not well-suited for many modern architectures, due to their bulky and rigid structure, and reduced performance in diffuse sunlight conditions. Luminescent solar concentrators (LSCs) provide a realistic solution to such limitations. LSCs are solar-harvesting devices fabricated using a transparent waveguide that is either doped or coated with luminescent species (lumophores). They can collect large areas of solar radiation and spectrally convert it to more useful energy via the process of photoluminescence (PL) of the embedded lumophores. The PL emission is then redirected to the edges of the LSC where strips of solar cells are mounted to convert the light energy into electricity. LSCs work well under both diffuse and direct sunlight conditions, making them particularly desirable for use in built environment and regions with high cloud coverage. In addition, they are often available in a variety of colours and geometries, ideal for architectural design. Nevertheless, the optical performance of an LSC is often undermined by the effect of aggregation-caused quenching (ACQ), which occurs at high lumophore concentrations in solid waveguides. ACQ can be potentially overcome by using lumophores that exhibit aggregation-induced emission (i.e., AIEgens). The emission of AIEgens becomes enhanced, rather than quenched, in aggregated states due to restricted intramolecular rotation (RIM). This thesis aims to investigate the use of AIEgens in waveguides that are made using a family organic-inorganic hybrid materials, also known as ureasils to fabricate LSCs with improved efficiencies. In Chapter 3, the first part of this work, a green-emitting conjugated polymer (CP) with AIE characteristics was used in a di-branched ureasil (di-ureasil) at various concentrations. No ACQ was observed for the AIE-active CP at high concentrations and by mixing it with a red-emitting perylene dye at optimised concentration ratio, effective Fӧrster energy transfer (FRET) was observed between the two lumophores. Due to the extended light harvesting window and reduced reabsorption loss provided by the dual-lumophore system, the resulting FRET-based LSC showed a high internal photon efficiency of 20%. In Chapter 4, a silole-based AIEgen, was adopted as the lumophore in a di-ureasil waveguide. Two methods of incorporation were investigated, covalent grafting and physical dispersion, at different concentrations. Both methods of incorporation led to the AIE behaviour of the lumophore in the di-ureasil host and no ACQ occurred even at the highest doping concentration of 1.4 mM. Compared to physical dispersion, the AIEgen that is covalently grafted to the hybrid matrix showed improved dispersity that reduced scattering losses and enhanced RIM that led to higher photoluminescence quantum yields (PLQY). Moreover, the occurrence of FRET from the photo-active ureasil to the silole AIEgen was confirmed with time-resolved PL measurements as shown by the reduction in the lifetime of the ureasil donor. This synergetic interaction between the host and lumophore may improve the absorption efficiency and hence the overall performance of the corresponding LSC device. In Chapter 5, the same silole-based AIEgen was employed as the lumophore doped in ureasil matrices with different organic backbones via covalent grafting. The effect of the organic structure of the ureasil matrix on the photophysical properties of the resulting AIEgen-ureasil material was investigated and the chain length of the polymer backbone was found to be the major factor. A shorter organic chain leads to a higher density of emitters in the siliceous and urea domain, and hence higher PLQY of the photo-active hybrid host. The FRET efficiency was also shown to be the highest between the ureasil with the shortest organic chain and the AIEgen. The AIEgen-ureasil system with optimised organic structure and concentration was fabricated then into a prototype LSC device. This was further mixed with a red-emitting perylene to create another FRET system, in order to shift the emission of the AIEgen further to the red region and increase the overall solar-harvesting range of the resulting LSC. The final AIEgen-based FRET LSC exhibited external and internal photon efficiencies of 9.0% and 29.3%, respectively, which are comparable to some of the most recent LSC designs reported in the literature. In summary, this work demonstrates a viable approach to mitigating the optical losses, including ACQ and reabsorption, for developing a new generation of LSCs with high optical performance. Moreover, the facile and versatile nature of the sol-gel process used to fabricate the hybrid material offers the possibility of designing LSCs with tunable optical and physical properties. Such results have undoubtably shown the great potential of AIE-active lumophores, in combination with ureasil hybrid waveguide, to advance the development of solar-harvesting systems that can be eventually integrated into the urban built environment

Förster Resonance Energy Transfer in Luminescent Solar Concentrators.

Luminescent solar concentrators (LSCs) are an emerging technology to collect and channel light from a large absorption area into a smaller one. They are a complementary technology for traditional solar photovoltaics (PV), particularly suitable for application in urban or indoor environments where their custom colors and form factors, and performance under diffuse light conditions may be advantageous. Förster resonance energy transfer (FRET) has emerged as a valuable approach to overcome some of the intrinsic limitations of conventional single lumophore LSCs, such as reabsorption or reduced quantum efficiency. This review outlines the potential of FRET to boost LSC performance, using highlights from the literature to illustrate the key criteria that must be considered when designing an FRET-LSC, including both the photophysical requirements of the FRET lumophores and their interaction with the host material. Based on these criteria, a list of design guidelines intended to aid researchers when they approach the design of a new FRET-LSC system is presented. By highlighting the unanswered questions in this field, the authors aim to demonstrate the potential of FRET-LSCs for both conventional solar-harvesting and emerging LSC-inspired technologies and hope to encourage participation from a diverse researcher base to address this exciting challenge

Research data supporting "Aggregation-induced emission from silole-based lumophores embedded in organic–inorganic hybrid hosts"

The folder “Figure 2” contains (2a) normalised UV/Vis absorption (20 μM in THF) and emission (20 μM in 10:90 by vol% THF/H2O) spectra data of DMTPS and DMTPS-Sil. The emission spectra were recorded at front face configuration, with excitation wavelength (λex) of 370 and 390 used for DMTPS and DMTPS-Sil, respectively. Emission spectra data of (2b) DMTPS (λex = 370 nm) and (2c) DMTPS-Sil (λex = 390 nm) measured in pure THF and 10:90 (v/v) THF/H2O mixture. The folder “Figure 3” contains the raw data for the normalised mean intensity extracted from the histograms of confocal microscopy images recorded throughout the gelation process using lase excitation of 405 nm (for DMTPS-d-UPTES and DMTPS-Sil-d-UPTES mixtures) and 488 nm (for LR305-d-UPTES mixture). The folder “Figure 4” contains the normalised emission spectra data of (4c) DMTPS (λex = 370 nm) and (4d) DMTPS-Sil (λex = 390 nm) in 10:90 (v/v) THF/H2O solvent mixture and dU(600) at concentrations of 0.014mM, 0.14 mM and 1.4 mM. The UV/Vis/NIR transmittance spectra data of (4e) DMTPS-dU(600)-x and (4f) DMTPS-Sil-dU(600)-x sample series. The folder “Figure 5” contains the data for TCSPC instrument response function, emission decay curves and the corresponding fits and residuals of (5a) DMTPS-Sil-dU(600)-x and (5b) DMTPS-dU(600)-x sample series upon excitation at 375 nm and detection of the emission decay curves at 600 nm. The pre-exponential factor, αi, associated with the emission decay of (4c) DMTPS-Sil-dU(600)-x and (4d) DMTPS-dU(600)-x sample series. The folder “Figure 6” contains the data for TCSPC instrument response function, emission decay curves and the corresponding fits and residuals of DMTPS-Sil-dU(600)-x sample series upon excitation at 375 nm and detection of the emission decay curves at 390 nm. The folder “Figure S5” contains the FTIR spectra data of the precursor Jeffamine ED-600, ICPTES and their product d-UPTES. The folder “Figure S9” contains data for the normalised emission spectra of the filtered acetone solution used to immerse (S9b) DMTPS-dU(600) and dU(600) (λex = 370 nm) and (S9d) DMTPS-Sil-dU(600) and dU(600) (λex = 390 nm). The folder “Figure S10” contains the data for the normalised emission spectra of acetone as a function of excitation wavelength under ambient conditions. The folder “Figure S11” contains the data for TCSPC instrument response function, emission decay curves and the corresponding fits and residuals of (S11a) DMTPS-Sil and (S11b) DMTPS in THF and 10:90 (v/v) THF/H2O solvent mixture upon excitation at 375 nm and detection of the emission decay curves at 600 nm. The folder “Figure S12” contains the data for TCSPC instrument response function, emission decay curves and the corresponding fits and residuals of DMTPS-Sil-dU(600)-x sample series upon excitation at 450 nm and detection of the emission decay curves at 620 nm. The folder “Figure S13” contains the data for the normalised excitation and emission spectra of dU(600) and the normalised absorption and emission spectra of DMTPS-Sil measured in 10:90 (v/v) THF:H2O solvent mixture at a concentration of 20 μM

Luminescent Solar Concentrators Based on Energy Transfer from an Aggregation-Induced Emitter Conjugated Polymer

Luminescent solar concentrators (LSCs) are solar-harvesting devices fabricated from transparent waveguide that is doped or coated with lumophores. Despite their potential for architectural integration, the optical efficiency of LSCs is often limited by incomplete harvesting of solar radiation and aggregation-caused quenching (ACQ) of lumophores in the solid state. Here, we demonstrate a multi-lumophore LSC design which circumvents these challenges through a combination of non-radiative Förster energy transfer (FRET) and aggregation-induced emission (AIE). The LSC incorporates a green-emitting poly(tetraphenylethylene), p-O-TPE, as an energy donor and a red-emitting perylene bisimide molecular dye (PDI-Sil) as the energy acceptor, within an organic-inorganic hybrid di-ureasil waveguide. Steady-state photoluminescence studies demonstrate that the di-ureasil host induced AIE from the p-O-PTE donor polymer, leading to a high photoluminescence quantum yield (PLQY) of ~45% and a large Stokes shift of ~150 nm. Covalent grafting of the PDI-Sil acceptor to the siliceous domains of the di-ureasil waveguide also inhibits non-radiative losses by preventing molecular aggregation. Due to the excellent spectral overlap, FRET was shown to occur from p-O-TPE to PDI-Sil, which increased with acceptor concentration. As a result, the final LSC (4.5 cm x 4.5 cm x 0.3 cm) with an optimised donor- acceptor ratio (1:1 by wt%) exhibited an internal photon efficiency of 20%, demonstrating a viable design for LSCs utilising an AIE-based FRET approach to improve the solar-harvesting performance.</div

Aggregation-induced emission from silole-based lumophores embedded in organic-inorganic hybrid hosts.

Aggregation-induced emitters - or AIEgens - are often symbolised by their photoluminescence enhancement as a result of aggregation in a poor solvent. However, for some applications, it is preferable for the AIE response to be induced in the solid-state. Here, the ability of an organic-inorganic hybrid polymer host to induce the AIE response from embedded silole-based lumophores has been explored. We have focussed on understanding how the incorporation method controls the extent of lumophore aggregation and thus the associated photophysical properties. To achieve this, two sample concentration series have been prepared, based on either the parent AIEgen 1,1-dimethyl-2,3,4,5-tetraphenylsilole (DMTPS) or the silylated analogue (DMTPS-Sil), which were physically doped or covalently grafted, respectively, to dU(600) - a member of the ureasil family of poly(oxyalkylene)/siloxane hybrids. Steady-state and time-resolved photoluminescence measurements, coupled with confocal microscopy studies, revealed that covalent grafting leads to improved dispersibility of the AIEgen, reduced scattering losses, increased photoluminescence quantum yields (up to ca. 40%) and improved chemical stability. Moreover, the ureasil also functions as a photoactive host that undergoes excitation energy transfer to the embedded DMTPS-Sil with an efficiency of almost 70%. This study highlights the potential for designing complex photoluminescent hybrid polymers exhibiting an ehanced AIE response for solid-state optical applications