Modulating electron injection from an organic dye to a titania nanoparticle with a photochromic energy transfer acceptor

We have prepared titania nanoparticles with an organic dye sensitiser and diarylethene molecular switch attached to the surface. Spectroscopic investigations show that the dye sensitiser's electron injection efficiency is reduced when the diarylethene is switched from its colourless, ring-open isomer to its coloured, ring-closed isomer, due to the introduction of a competing energy transfer pathway

Plasticiser leaching from polyvinyl chloride microplastics and the implications for environmental risk assessment

Microplastics in aquatic environments is a growing concern, particularly due to the leaching of chemical additives such as plasticisers. To develop comprehensive environmental risk assessments (ERAs) of high-concern polymers and plasticisers, an understanding of their leachability is required. This work investigated diethylhexyl phthalate (DEHP) and bisphenol A (BPA) leaching from polyvinyl chloride (PVC) microplastics (average diameter = 191 μm) under simulated marine conditions. Leaching behaviours were quantified using gel permeation chromatography (GPC) and thermal gravimetric analysis (TGA), and the polymer's physiochemical properties analysed using differential scanning calorimetry (DSC), Fourier Transform-Infrared Spectroscopy (FT-IR) and optical microscopy. Experimental data were fitted to a diffusion and boundary layer model, which found that BPA leaching was temperature-dependent (diffusion-limited), whereas DEHP leaching was controlled by surface rinsing. Model predictions also highlighted the importance of microplastic size on leaching dynamics. These data contribute towards greater accuracy in ERAs of microplastics, with implications for water quality and waste management, including decommissioning of plastic infrastructure

Photochrome-doped organic films for photonic key-pad locks and multi-state fluorescence

The spectroscopic properties of poly(methyl methacrylate) polymer films doped with two kinds of photochromic molecular switches are investigated. A green-fluorescent sulfonyl diarylethene (P1) is combined with either a non-fluorescent diarylethene (P2) or red-fluorescent spiropyran (P3). Photoswitching between the colorless and colored isomers (P1: o-BTFO4 ↔ c-BTFO4, P2: o-DTE ↔ c-DTE, P3: SP ↔ MC) enables the P1+P2 and P1+P3 films to be cycled through three distinct states. From the initial state (o-BTFO4 + o-DTE/SP), irradiation with UV light generates the second state (c-BTFO4 + c-DTE/MC), where c-BTFO4 → c-DTE/MC energy transfer is established. Irradiation with green light then generates the third state (c-BTFO4 + o-DTE/SP), where the energy transfer acceptor is no longer present. Finally, irradiation with blue light regenerates the initial state. For the P1+P2 film, only one state is fluorescent, with the irradiation inputs required to be entered in the correct order to access this state, acting as a keypad lock. For the P1+P3 film, the states emit either no fluorescence, red fluorescence, or green fluorescence, all using a common excitation wavelength. Additionally, once the fluorescence is activated with UV light, it undergoes a time-dependent color transition from red to green, due to the pairing of P-type and T-type photochromes. These multi-photochromic systems may be useful for security ink or imaging applications

Oil spill source identification using colorimetric detection

The colorimetric detection of polycyclic aromatic hydrocarbons (PAHs) was investigated for the quick and easy identification of likely oil spill offenders. In this new technology, photochromic compounds were used to sense PAHs by varying their photoswitching capacity. To that end, three photochromes were designed and showed varying degrees of photoswitching inhibition depending on PAH analyte, photochrome and excitation wavelength. PAH mixtures that mimic oil spills showed the same varying response and demonstrated the accuracy of this technology. To prove the applicability of this technology, an array was assembled using the three photochromes at three excitation wavelengths and tested against authentic crude oil samples. Not only could these samples be differentiated, weathering of two distinctly different oil samples showed limited variation in response, demonstrating that this may be a viable technique for in situ oil identification

The effect of the phenylene linkage in poly(fluorene-alt-phenylene)s on the thermodynamics and kinetics of nitroaromatic and nitroaliphatic sensing

The preparation, photophysical characterization and sensing of a series of highly luminescent poly(fluorene-alt-phenylene)s (PFP) were studied. These PFP polymers varied the phenylene linkage in the 1,4 (PFP-p), 1,3 (PFP-m) and 1,2 (PFP-o) positions. The photoluminescence of these polymers ranged from ultraviolet to blue in color in both solution and film states by simply varying the linkage of the phenylene moiety. Photon Electron Spectroscopy in Air (PESA) revealed that the change in the emission was primarily attributed to the difference of the electron affinity of the polymer. Stern-Volmer quenching studies indicated that these poly(fluorene-alt-phenylene) polymers are highly sensitive towards nitroaromatic materials in solution, particularly in comparison to the reference poly(9,9-di-n-hexylflourene) (PDHF). These PFP polymers were found to be four to ten times more sensitive towards dinitrobenzene as compared to PDHF. In addition, PFP-o displayed the highest polymer-based Stern-Volmer quenching towards the taggant DMNB. The solid-state fluorescence quenching of the PFP-p and PFP-m films using DMNB was enhanced (up to 71.5%) compared to the reference PDHF (59.6%) and was attributed to both thermodynamic and diffusion kinetic factors

Evaluating the Effect of Chemical Digestion Treatments on Polystyrene Microplastics: Recommended Updates to Chemical Digestion Protocols

Establishing the toxicity and exposure consequences of microplastics (MPs) on marine organisms relies on the nondestructive isolation of plastics from biological matrices. MPs are commonly extracted from these matrices by chemical digestion using alkali (e.g., potassium hydroxide (KOH) and sodium hydroxide (NaOH)), oxidative (e.g., hydrogen peroxide (H2O2)) and/or acidic (e.g., nitric acid (HNO3)) reagents. Although these digestion conditions can be highly effective for MP extraction, they can also react with the plastics. This can attribute an inaccurate representation of plastic contamination by altering MP visual characteristics (size, shape, color), thereby impeding identification and potentially returning erroneous numbers of ingested particles. In this study, the degradative impacts are assessed of the routinely applied digestion reagents (i) KOH, (ii) NaOH, (iii) H2O2, and (iv)HNO3 on polystyrene (PS) based MPs sized between 200 μm and 5 mm. Degradation of the PS MPs is evaluated using FT-IR, gel permeation chromatography, NMR, photoluminescence spectroscopy, and microscopy. These studies reveal HNO3 to be the most destructive for PS MPs, while the alkali and oxidative reagents result in negligible changes in plastic properties. These results are recommended to be used as a guideline to update current protocols to ensure the nondestructive treatment of MPs

Synthesis, Photo- and Electro- Optical Properties of Luminescent Pi-conjugated Polymers

The focus of this work is the synthesis, structure, and luminescent properties of n-conjugated polymers. The polymer properties may be tailored with various functional groups, resulting in an increase of emission efficiency and colour tunability. These polymers are important since polymer light emitting diodes (PLEDs) may be used in the production of next generation displays. For this reason, it is important understand the structure-property relationships of luminescent n-conjugated polymers, and their spatial controlled deposition. Three classes of luminescent n-conjugated polymers are investigated herein - poly(3-alkylthiophene)~ (P~ATs), poly(phenyleneviny1ene) (PPVs), and poly(fluorene-co-thiophene) (PFTs). Their structure-property relationships were studied by post-functionalization and host-guest type methodologies. Post-functionalization - via electrophilic aromatic substitution - of P3AT and PPV was efficient, and provided a precise method to control the effective conjugation length. Further post-functionalization of the P3AT system via Pdcatalyzed cross coupling proved effective for obtaining a plethora of 3,4- disubstituted P3ATs. It was found that sterically encumbered groups increased the luminescence efficiency by increasing the interlayer distance between the polymer chains. Alternating poly(fluorene-co-thiophene)~ were prepared with 2,5-, 2,4- and 3,4-thiophene linkages. The type of thiophene linkage had a dramatic effect on the emission colour - from UV emitting to green - while little effect was observed for the emission efficiency. Since the strong spectral overlap between the emission of the 3,4-linked PFT with the absorption of 2,5-linked PFT, and the molecular similarity, host-guest systems via blending and copolymerization was investigated. In an effort to obtain high energy emission, a PFT with 2,7-linked fluorene as the guest in a 3,4-linked PFT host were also investigated. Tetrahydropyan (THP) bearing conjugated polymers have proven useful for obtaining spatial controlled deposition. Since these polymers are important for high resolution displays, the photo-physics of these polymers were investigated. Two classes of THP-containing conjugated polymers were studied; namely, P3ATs and PFTs. For P3ATs, it was found that shorter alkyl chain spacers enhanced the emission efficiency and tuned the emission colour. Upon thermolytic cleavage of the THP group, the luminescence efficiency decreased dramatically. Since PFTs are inherently more luminescent than P3ATs, PFTs bearing THP-groups were also investigated

Provisional specification for the invention entitled: An apparatus and a method of detecting the presence of an analyte

[Extract] Field of the Invention: The present invention relates to analyte detection and in particular to an\ud apparatus and a method of detecting the presence of an analyte

Colorimetric detection of nitroaromatics using organic photochromic compounds

An organic photochromic compound is explored as a new portable colorimetric sensor for nitroaromatics. This photochromic compound switches from colourless to pink upon exposure to ultraviolet light. In the presence of nitroaromatic explosive derivatives the photoswitching behaviour of the dithienylethene is suppressed, while a potential false positive (toluene) has little effect. The degree of photoswitching inhibition was determined by comparing the integrated visible absorption with the concentration of the analyte to give the pseudo Stern–Volmer constant (K(PSV)). The K(PSV)s measured varied from 12900 (p-nitrotoluene) to 236 M^–1 (toluene), which were directly related to the analyte absorption at the excitation wavelength