Vapochromic features of new luminogens based on julolidine-containing styrene copolymers

We report on vapochromic films suitable for detecting volatile organic compounds (VOCs), based on new polystyrene copolymers containing julolidine fluorescent molecular rotors (JCAEM). Poly(styrene-co-hydroxyethylmethacrylate) copolymers functionalized with cyanovinyl-julolidine moieties of different compositions were prepared, (P(STY-co-JCAEM)(m) with m = 0.06-0.61). The sensing performance of the spin-coated copolymer films demonstrated significant vapochromism when exposed to VOCs characterized by high vapour pressure and a favourable interaction with the polymer matrix, such as Et2O and CH2Cl2. It is worth mentioning that the fluorescence decrease rate was 7 times faster than that of previously investigated julolidine-based fluorescent molecular rotors dispersed in PS films. This phenomenon was attributed to the better control of the JCAEM moiety distribution in the polymer matrix conferred by the covalent approach, combined with a minimal film thickness of 4 microns. These factors, in concert, strongly accelerate the deactivation pathways of the JCAEM units in the presence of VOCs which interact well. Overall, the present results support the use of julolidine-enriched styrene copolymers as effective chromogenic materials suitable for the fast detection of VOCs

Julolidine fluorescent molecular rotors as vapour sensing probes in polystyrene films

We introduce a new sensing polymer system for detection of volatile organic compounds (VOCs) based on the optical response of polystyrene (PS) films doped with julolidine fluorescent molecular rotors (FMRs). The julolidine FMRs exhibited viscosity-dependent changes in the fluorescence intensity, that was enhanced when glycerol was added to ethanol solutions and when they were dispersed in PS films. Thus, reduction in medium mobility slowed down internal motions and allowed for a major radiative decay pathway. The FMR/PS films were exposed to several VOCs, and showed a significant decrease in fluorescence emission when exposed to chloroform, whereas a negligible variation in their emission occurred when methanol was utilized. This vapour sensing behaviour was much more evident when a perfluorodecyl chain was linked to the julolidine core being the molecule segregated at the film surface. This responsive behaviour was affected by solvent composition and its reproducible response was easily determined by luminescence experiments

Exploring the impact of structural rigidification of amino-substituted bio-inspired flavylium dyes in DSSCs

Publisher Copyright: © 2023 The AuthorsSharing with anthocyanins the 2-phenyl-1-benzopyrylium structural motif, flavylium derivatives are strongly colored bio-inspired dyes that have been explored in dye-sensitized solar cells (DSSCs). Following on the fact that the most efficient flavylium-based dyes for DSSCs require amine electron-donating groups, a diethylamino group and the corresponding rigidified julolidine group were introduced in the benzopyrylium core. This structural variation was combined with another structural parameter – increased planarization of the flavylium ring system – to yield four flavylium derivatives all with a catechol anchoring group. The several pKa values of the new dyes and the UV–vis absorption data at different pH values and upon adsorption to TiO2 (corroborated by TD-DFT calculations) demonstrate a stronger delocalization of the nitrogen lone pair in the julolidine systems when compared to the diethylamino ones, reflecting the stronger electron-donating ability of the former. However, the julolidine-based dyes resulted in a decrease in all DSSC parameters, with efficiencies of 0.6% vs. 2.3% for the diethylamino devices. Discarding eventual increased self-aggregation processes of the more planar julolidine derivatives through studies with a de-aggregating agent (CDCA), and determining comparable dye loadings for all dyes, the presence of increased back-electron transfer processes for the julolidine-based compounds is advanced to explain their lower efficiencies. Rigidification of the flavylium dyes by bridging the benzopyrylium and the phenyl rings is demonstrated by higher fluorescence quantum yields and by electrochemical data and leads to a slight increase in the efficiency of the respective DSSCs. The results contribute to consolidate the potential of flavylium dyes as sensitizers for DSSCs.publishersversionpublishe

Metal directed supramolecular assemblies for optical materials : chemosensor design and application

This dissertation reports the design, synthesis and characterisation of several metallosupramolecular assemblies incorporating 8-hydroxyjulolidine-9-carboxaldehyde or 4- (diethylamino)salicylaldehyde groups. These groups are well known as strong electron donors, and as such, they are potentially favourable for the development of electro-optical materials, especially chemosensors. Furthermore, the presence of their aldehyde functional group makes these moieties ideal for condensation reactions with primary amines, and the resulting imine (chapter 2-4) or dihydropyrimidine (chapter 5-7) groups are situated near the OH of the phenol groups; thus the synthesised ligand has an ideal preorganised polydentate coordination environment. In this dissertation, several supramolecular assemblies based on either 8-hydroxyjulolidine- 9-carboxaldehyde or the 4-(diethylamino)salicylaldehyde group were investigated by a range of techniques, including NMR, FT-IR, ESI-HRMS, SEM-EDS, Raman, STA, UVVis and fluorescence spectroscopy. In addition to these techniques, 13 crystal structures were also determined by SC-XRD using the MX1 and MX2 beamlines at the Australian Synchrotron. These structures showed various conformations, many of which are mediated by the coordinating metal ions, anions, and the experimental conditions, etc. Furthermore, two ligands show great potential as chemosensors for nanomolar colourimetric detection of Cu2+, and a protocol has been developed for colourimetric detection of exchangeable Cu2+ on soils

Reversible photoswitching of isolated ionic hemiindigos with visible light

Indigoid chromophores have emerged as versatile molecular photoswitches, offering efficient reversible photoisomerization upon exposure to visible light. Here we report synthesis of a new class of permanently charged hemiindigos (HIs) and characterization of photochemical properties in gas phase and solution. Gas-phase studies, which involve exposing mobility-selected ions in a tandem ion mobility mass spectrometer to tunable wavelength laser radiation, demonstrate that the isolated HI ions are photochromic and can be reversibly photoswitched between Z and E isomers. The Z and E isomers have distinct photoisomerization response spectra with maxima separated by 40–80 nm, consistent with theoretical predictions for their absorption spectra. Solvation of the HI molecules in acetonitrile displaces the absorption bands to lower energy. Together, gas-phase action spectroscopy and solution NMR and UV/Vis absorption spectroscopy represent a powerful approach for studying the intrinsic photochemical properties of HI molecular switches

Fluorescent Polystyrene Films for the Detection of Volatile Organic Compounds Using the Twisted Intramolecular Charge Transfer Mechanism

Thin films of styrene copolymers containing fluorescent molecular rotors were demonstrated to be strongly sensitive to volatile organic compounds (VOCs). Styrene copolymers of 2-[4-vinyl(1,1'-biphenyl)-4'-yl]-cyanovinyljulolidine (JCBF) were prepared with different P(STY-co-JCBF)(m) compositions (m% = 0.10-1.00) and molecular weights of about 12,000 g/mol. Methanol solutions of JCBF were not emissive due to the formation of the typical twisted intramolecular charge transfer (TICT) state at low viscosity regime, which formation was effectively hampered by adding progressive amounts of glycerol. The sensing performances of the spin-coated copolymer films (thickness of about 4 µm) demonstrated significant vapochromism when exposed to VOCs characterized by high vapour pressure and favourable interaction with the polymer matrix such as THF, CHCl₃ and CH₂Cl₂. The vapochromic response was also reversible and reproducible after successive exposure cycles, whereas the fluorescence variation scaled linearly with VOC concentration, thus suggesting future applications as VOC optical sensors

Development of a fluorescence based viscosity sensor for medical applications

Abstract only availableThe purpose of this project is to determine the binding properties of molecular rotors with macromolecules, specifically plasma proteins. This is to aid in the development of a viscometer based on molecular rotors that could be used on blood plasma by determining to what effect the presence of these proteins will affect the measurements of the viscometer so that it may be put into use in the medical field. Molecular rotors are a class of florescent molecules that form a twisted internal charge transfer complex upon excitation, they have a preferred de-excitation pathway of rotation about a C=C double bond. When molecular free volume is limited, rotation about this bond is hindered and fluorescence probability increases. The intensity of the fluorescence of these molecules can be used as a measure of the viscosity of the solvent. Intensity and viscosity are related by the following equation: log F = C + x log h where F is the fluorescent yield, h is the viscosity, and x and C are constants. The rotors in this study are CCVJ (9-[(2-Cyano-2-hydroxy carbonal) vinyl] julolidine) and CCVJ-TEG (9-[(2-Cyano-2-hydroxy carbonal) vinyl] julolidine triethyleneglycol). The affinity of these molecular rotors to various plasma proteins is determined by comparing the solubility of the molecular rotors in proteinaceous and nonproteinaceous solutions. The molecular rotors are allowed to diffuse through a dialysis membrane until the equilibrium between the two solutions is reached. The concentration of the rotors in the solutions was determined by measuring the absorbance of these solutions according to the Beer-Lambert law: A= e * c where A is absorbance, e is the extinction coefficient of the specific substance at the specific wavelength, and c is the concentration of that substance. The proteins tested in this manner were albumin, fibrinogen, and IgG. Bovine proteins were used because all mammalian proteins are very similar and bovine proteins are easier to obtain than human proteins. The results show that CCVJ and CCVJ-TEG are very strongly attracted to Albumin, and weakly attracted to fibrinogen. This attraction may affect the fluorescence of the rotor molecules, meaning that in developing these molecular rotors as viscosity sensors for blood plasma, further studies must be performed to determine the effect of the proteins on the fluorescent behavior of the rotors so that the protein composition of the plasma can be accounted for.Life Sciences Undergraduate Research Opportunity Progra