A fluorescent thermometer based on a pyrene-labeled thermoresponsive polymer

Effects Induced by the Temperature and Chemical Environment on the Fluorescence of Water-Soluble Gold Nanoparticles Functionalized with a Perylene-Derivative Dye

We developed a fluorescent molecular probe based on gold nanoparticles functionalized with N,N'-bis(2-(1-piperazino)ethyl)-3,4,9,10-perylenetetracarboxylic acid diimide dihydrochloride, and these probes exhibit potential for applications in microscopic thermometry. The intensity of fluorescence was affected by changes in temperature. Chemical environments, such as different buffers with the same pH, also resulted in different fluorescence intensities. Due to the fluorescence intensity changes exhibited by modified gold nanoparticles, these materials are promising candidates for future technologies involving microscopic temperature measurements.

Gated Photoreactivity of Pyrene Copolymers in Multiresponsive Cross-Linked starPEG-Hydrogels

The synthesis and manufacturing of multiresponsive polymer hydrogels using simple components is a notable challenge. Pyrene is an excimer-forming fluorophore mostly used as microenvironmental probe and for the localization of molecules in close proximity in artificial and biomaterials. Here we make use of the solvophobic preaggregation and photolysis properties of pyrene to construct multiresponsive hydrogels. We synthesize poly(ethylene glycol) (PEG) hydrogels from well-defined pyrene-substituted macro-cross-linkers and elucidate their intricate intra- and intermolecular excimer formation pathways. We find that controlling the water content of the hydrogels through the degree of swelling acts as a gating stimulus governing the photoinduced solvolysis of pyrenylmethyl esters from their poly(methacrylate) backbone. This allows the implementation of a simple transient photolithography process. We thus demonstrate that multiresponsive soft materials with complex optical and mechanical responses can be obtained with comparatively little synthetic effort.

Comparative study of the photophysical and crystallographic properties of 4-(9H-pyreno[4,5-d]imidazol-10-yl)phenol and its alkylated derivatives

The photophysical and crystallographic properties of a para-hydroxphenyl-substituted pyrenoimidazole and its decylated analogues were investigated. The fluorescence of these compounds is sensitive to environmental acidity and basicity.

Hybrid Fluorescent Poly(silsesquioxanes) with Amide- and Triazole-Containing Side Groups for Light Harvesting and Cation Sensing

Hybrid polymers containing pyrene (Py) units bound to linear poly(silsesquioxane) (LPSQ) chains through flexible linkers containing heteroatoms (S, N, O) (LPSQ-triazole-Py and LPSQ-amide-Py) exhibit intense fluorescence emission, both in very diluted solutions (c = 10-8 mol/L) and in the solid state. The materials are thermally stable and exhibit good thin film forming abilities. Their optical and physicochemical properties were found to be strongly dependent on the structure of the side chains. Comparative studies with octahedral silsesquioxane (POSS) analogues (POSS-triazole-Py and POSS-amide-Py) emphasized the role of the specific double-strand architecture of the LPSQ backbone and distribution of side Py groups for their photo-luminescent properties. The new hybrid materials were tested as fluorescence energy donors to red-emitting dyes (Nile Red and Coumarine 6). All the silsesquioxanes studied were found to be able to transfer FL emission energy to Coumarin 6, irrespectively of their spatial structure. However, due to the differences in the wavelength range of FL emission, only LPSQ-triazole-Py were able to act as energy donors to Nile Red. The Py-grafted LPSQ may be also applied for development of soluble and highly emissive chemosensors. Their fluorescent nature was explored for the detection of Cu(II), Fe(III), Co(II), Ag(I), Hg(II), Mg(II), Ca(II), Pb(II) and Zn(II). The morphology of the side chains and hydrogen-bonding interactions influenced the sensing capacity of all the studied materials.

Influence of Cyclodextrins on Thermosensitive and Fluorescent Properties of Pyrenyl-Containing PDMAA

A series of pyrenyl-containing PDMAA copolymers were prepared by free radical copolymerization of dimethylacrylamide (DMAA) with pyrenebutanoyloxy ethyl methacrylate (PyBEMA). The structure of as-prepared copolymers was characterized by UV, FT-IR and 1H NMR spectroscopy. The effect of cyclodextrins (α-CD, β-CD and γ-CD) on the thermosensitivity and fluorescence of the copolymers in aqueous solutions were investigated. It was found that the as-prepared copolymers exhibit lower critical solution temperature (LCST)-type thermosensitivity. Cloud point (Tcp) decreases with the increasing molar content of PyBEMA unit in the copolymers. Tcp of the copolymers increases after the CD is added from half molar to equivalent amount relative to pyrenyl moiety, and that further adding twice equivalent CD results in a slight decrease in Tcp. The copolymers exhibit a pyrene emission located at 377 nm and a broad excimer emission centered at 470 nm. The copolymers in water present a stronger excimer emission (Intensity IE) relative to monomer emission (Intensity IM) than that in ethanol. The IE/IM values decrease after the addition of equivalent α-CD, β-CD and γ-CD into the copolymers in aqueous solution, respectively. The IE/IM values abruptly increase as the copolymers' concentration is over 0.2 mg/L whether in ethanol solution or aqueous solution with or without CD, from which can probably be inferred that intra-polymeric pyrene aggregates dominate for solution concentration below 0.2 mg/L and inter-polymeric pyrene aggregates dominate over 0.2 mg/L. Furthermore, the formation of the CD pseudopolyrotaxanes makes it possible to form pyrene aggregates. For high concentration of 5 g/L, the copolymers and their inclusion complexes completely exhibit an excimer emission. The IE values abruptly increased as the temperature went up to Tcp, which indicates that the IE values can be used to research phase separation of polymers.

In Situ Monitoring of Fluorescent Polymer Brushes by Angle-Scanning Based Surface Plasmon Coupled Emission

Fluorescent polymers have attracted interest in many fields such as sensing, diagnostics, imaging, and organic electronic devices. Real-time techniques to monitor and understand the polymerization process are important for obtaining controllable fluorescence polymers. We present a new technique to in situ monitor the growth process of fluorescent polymer brushes by using angle-scanning based surface plasmon coupled emission (AS-SPCE) approach during electrochemically mediated atom-transfer radical polymerization. The polymer thickness was determined by modeling the location of SPCE emission angle(s) with theoretical calculation. The advantages of unique angle distribution patterns, thickness dependence and effective background rejection of AS-SPCE guarantee the success in the real-time investigation for controllable fabrication of fluorescent polymers.

Understanding the effect of monomer structure of oligoethylene glycol acrylate copolymers on their thermoresponsive behavior for the development of polymeric sensors

Oligoethylene glycol acrylate (OEGA) polymers are a class of thermoresponsive polymers. Three new OEGA monomer combinations were investigated, which revealed three different types of thermoresponsive behavior as a function of copolymer composition.

pH-Responsive diblock copolymers with two different fluorescent labels for simultaneous monitoring of micellar self-assembly and degree of protonation

Facile labelling of both blocks of a pH-responsive diblock copolymer with different fluorophores allows monitoring of polymer aggregation and deprotonation.

A suitable (wide-range + linear) temperature sensor based on Tm3+ ions

Future advances in the broad fields of photonics, (nano-)electronics or even theranostics rely, in part, on the precise determination and control, with high sensitivity and speed, of the temperature of very well-defined spatial regions. Ideally, these temperature-sensors (T-sensors) should produce minimum (or no) disturbance in the probed regions, as well as to exhibit good resolution and significant dynamic range. Most of these features are consistent with the sharp and distinctive optical transitions of trivalent rare-earth (RE³⁺) ions that, additionally, are susceptible to their local environment and conditions. Altogether, these aspects form the basis of the present work, in which we propose a new T-sensor involving the light emission of trivalent thulium ions (Tm³⁺) embedded into crystalline TiO₂. The optical characterization of the TiO₂:Tm³⁺ system indicated a Tm³⁺-related emission at ~676 nm whose main spectral features are: (1) a temperature-induced wavelength shift of −2.2 pm K⁻¹, (2) a rather small line-width increase over the ~85–750 K range, and (3) minimum data deconvolution-processing. The study also included the experimental data of the well-established pressure- and T-sensor ruby (Al₂O₃:Cr³⁺) and a comprehensive discussion concerning the identification and the excitation-recombination mechanisms of the Tm³⁺-related transitions.

Schizophrenic poly(ε-caprolactone)s: synthesis, self-assembly and fluorescent decoration

Double hydrophilic copolymers PCCL-b-PPIL and their pyrene-modified copolymers showed pH-responsive “schizophrenic” aggregation behaviors.

Multiresponsive Behavior of Functional Poly(p-phenylene vinylene)s in Water

The multiresponsive behavior of functionalized water-soluble conjugated polymers (CPs) is presented with potential applications for sensors. In this study, we investigated the aqueous solubility behavior of water-soluble CPs with high photoluminescence and with a particular focus on their pH and temperature responsiveness. For this purpose, two poly(phenylene vinylene)s (PPVs)-namely 2,5-substituted PPVs bearing both carboxylic acid and methoxyoligoethylene glycol units-were investigated, with different amount of carboxylic acid units. Changes in the pH and temperature of polymer solutions led to a response in the fluorescence intensity in a pH range from 3 to 10 and for temperatures ranging from 10 to 85 °C. Additionally, it is demonstrated that the polymer with the largest number of carboxylic acid groups displays upper critical solution temperature (UCST)-like thermoresponsive behavior in the presence of a divalent ion like Ca2+. The sensing capability of these water-soluble PPVs could be utilized to design smart materials with multiresponsive behavior in biomedicine and soft materials.

Smart Homopolymer Microgels: Influence of the Monomer Structure on the Particle Properties

In this work, we compare the properties of smart homopolymer microgels based on N-n-propylacrylamide (NNPAM), N-isopropylacrylamide (NIPAM) and N-isopropylmethacrylamide (NIPMAM) synthesized under identical conditions. The particles are studied with respect to size, morphology, and swelling behavior using scanning electron and scanning force microscopy. In addition, light scattering techniques and fluorescent probes are employed to follow the swelling/de-swelling of the particles. Significant differences are found and discussed. Poly(N-n-propylacrylamide) (PNNPAM) microgels stand out due to their very sharp volume phase transition, whereas Poly(N-isopropylmethacrylamide) (PNIPMAM) particles are found to exhibit a more homogeneous network structure compared to the other two systems.

A fluorescent acrylamide-type monomer bearing an environment-sensitive methoxybenzocoumarin structure for the development of functional polymeric sensors

A new fluorescent acrylamide-type monomer bearing a hydrogen bonding- and polarity-sensitive benzocoumarin fluorophore was synthesized and applied for developing a fluorescent polymeric thermometer.

Thermoresponsive interplay of water insoluble poly(2-alkyl-2-oxazoline)s composition and supramolecular host-guest interactions

A series of water insoluble poly[(2-ethyl-2-oxazoline)-ran-(2-nonyl-2-oxazoline)] amphiphilic copolymers was synthesized and their solubility properties in the presence of different supramolecular host molecules were investigated. The resulting polymer-cavitand assemblies exhibited a thermoresponsive behavior that could be modulated by variation of the copolymer composition and length. Interestingly, the large number of hydrophobic nonyl units across the polymer chain induced the formation of kinetically-trapped nanoparticles in solution. These nanoparticles further agglomerate into larger aggregates at a temperature that is dependent on the polymer composition and the cavitand type and concentration. The present research expands the understanding on the supramolecular interactions between water insoluble copolymers and supramolecular host molecules.

Macro-/micro-environment-sensitive chemosensing and biological imaging

We have summarized the research progress on fluorescent sensors responsive to environmental factors, including local viscosity, polarity, temperature, hypoxia and pH.

Thermometry at the nanoscale

Non-invasive precise thermometers working at the nanoscale with high spatial resolution, where the conventional methods are ineffective, have emerged over the last couple of years as a very active field of research. This has been strongly stimulated by the numerous challenging requests arising from nanotechnology and biomedicine. This critical review offers a general overview of recent examples of luminescent and non-luminescent thermometers working at nanometric scale. Luminescent thermometers encompass organic dyes, QDs and Ln(3+)ions as thermal probes, as well as more complex thermometric systems formed by polymer and organic-inorganic hybrid matrices encapsulating these emitting centres. Non-luminescent thermometers comprise of scanning thermal microscopy, nanolithography thermometry, carbon nanotube thermometry and biomaterials thermometry. Emphasis has been put on ratiometric examples reporting spatial resolution lower than 1 micron, as, for instance, intracellular thermometers based on organic dyes, thermoresponsive polymers, mesoporous silica NPs, QDs, and Ln(3+)-based up-converting NPs and β-diketonate complexes. Finally, we discuss the challenges and opportunities in the development for highly sensitive ratiometric thermometers operating at the physiological temperature range with submicron spatial resolution.

Polymeric assemblies and nanoparticles with stimuli-responsive fluorescence emission characteristics

Fluorescent polymeric assemblies and nanoparticles (NPs) of nanoscale dimensions have become a focus of intensive investigations during the past few decades due to combined advantages such as improved biocompatibility, water dispersibility, stimuli-responsiveness, facile integration into optical detection devices, and the ability of further functionalization. In addition, the chemical composition and morphology of polymeric assemblies and NPs can be modulated via synthetic approaches, leading to the precise spatial organization of multiple fluorophores. Thus, polymeric assemblies and NPs have been utilized to optimize the photoluminescent properties of covalently or physically attached fluorophores and facilely modulate the fluorescence resonance energy transfer (FRET) processes when the polymeric matrix is endowed with stimuli-responsiveness. These fascinating fluorescent polymeric assemblies and NPs offer unique and versatile platforms for the construction of novel detection, imaging, biolabeling, and optoelectronic systems. This feature article focuses on the recent developments of polymeric assemblies and NPs-based stimuli-tunable fluorescent systems and highlights their future practical applications with selected literature reports.

Aqueous polymeric sensors based on temperature-induced polymer phase transitions and solvatochromic dyes

This feature article provides, for the first time, an overview of the research that guided the way from fundamental studies of the thermo-responsive phase separation of aqueous polymer solutions to polymeric sensor systems. The incorporation of solvatochromic dyes into thermoresponsive polymers as well as the concepts of polymeric sensors are presented and discussed in detail.