Photophysics of preassociated pyrenes in aqueous polymer solutions and in other organized media

Assessing hydrophobic deep eutectic solvents for intramolecular excimer formation

Intramolecular excimer formation by a dipyrenyl probe, 6-(1-pyrenyl)hexyl-11(1-pyrenyl)-undecanoate [1-Py(CH2)10COO(CH2)61-Py], is used to assess hydrophobic deep eutectic solvents (HDESs) for the purpose. n-Decanoic acid (DA), L(-)-menthol (Men) and thymol (Thy) have been utilized to form HDESs with different pairs of constituents in different molar ratios, namely Men : DA (2 : 1, 1 : 1, and 1 : 2), Thy : DA (2 : 1, 1 : 1, and 1 : 2), and Thy : Men (5 : 1, 2 : 1, 1 : 1, 1 : 2, and 1 : 5). The maximum of the excimer-to-monomer emission intensity ratio, (IE/IM)max, is observed at 343.15-353.15 K for all DESs irrespective of the constitution, and it varies in a narrow range exhibiting no correlation with the dynamic viscosity (η) of the DES which varies between 2.05 and 3.56 mPa s. Excited-state intensity decay data reveal excimer dissociation back to the excited monomer to be negligible in all DESs at lower temperatures (T ≤ 323.15 K); the simplistic Birks scheme is followed at higher temperatures (T > 323.15 K). The rate constant for excimer formation/association, ka, ranges from (3.00 ± 0.50) × 106 s-1 to (103 ± 10) × 106 s-1, which is similar to that reported in other media. The temperature-dependence of the equilibrium constant for excimer formation follows the van't Hoff equation with recovered standard enthalpy (ΔaH*⊖) and standard entropy (ΔaS*⊖) changes, indicating the reversible intramolecular excimer formation to be exothermic and energetically-favorable but entropically unfavorable. A plot of kavs. T/η for all the DES systems investigated exhibits a fairly good linear correlation, indicating the adherence to the Stokes-Einstein formulation within the HDESs further emphasizing the homogeneous nature of the solubilizing media. The work helps to highlight the potential of HDESs for intramolecular excimer formation involving non-polar reactants.

Recent Advances in Electrochemiluminescence Biosensors for MicroRNA Detection

Electrochemiluminescence (ECL) as an analytical technology with a perfect combination of electrochemistry and spectroscopy has received considerable attention in bioanalysis due to its high sensitivity and broad dynamic range. Given the selectivity of bio-recognition elements and the high sensitivity of the ECL analysis technique, ECL biosensors are powerful platforms for the sensitive detection of biomarkers, achieving the accurate prognosis and diagnosis of diseases. MicroRNAs (miRNAs) are crucial biomarkers involved in a variety of physiological and pathological processes, whose aberrant expression is often related to serious diseases, especially cancers. ECL biosensors can fulfill the highly sensitive and selective requirements for accurate miRNA detection, prompting this review. The ECL mechanisms are initially introduced and subsequently categorize the ECL biosensors for miRNA detection in terms of the quenching agents. Furthermore, the work highlights the signal amplification strategies for enhancing ECL signal to improve the sensitivity of miRNA detection and finally concludes by looking at the challenges and opportunities in ECL biosensors for miRNA detection.

Exciplex Formation by Complexation of an Electron-Accepting Guest in an Electron-Donating Pillar[5]arene Host Liquid

We present a novel system, a liquid-state pillar[5]arene decorated with tri(ethylene oxide) chains, that brings electron-donor and electron-acceptor molecules into proximity for efficient exciplex formation. The electron-accepting guests exhibit a blue-purple emission from a localized excited state upon excitation in common solvents. However, directly dissolving the guests in the electron-donating pillar[5]arene liquid (a bulk system) results in visible green emission from the formed exciplexes. In the bulk system, the guest molecules are always surrounded by excess pillar[5]arene molecules, resulting in the formation of mainly inclusion-type exciplexes. In the bulk system, energy migration occurs between the pillar[5]arene molecules. Excitation of the pillar[5]arenes results in a more intense green exciplex emission than that observed upon direct excitation of the guests. In summary, the pillar[5]arene liquid is a novel system for achieving efficient exciplex formation and energy migration that is different from typical solvent and solid systems.

Dynamic Transition between Monomer and Excimer Phosphorescence in Organic Near-Infrared Phosphorescent Crystals

Achieving efficient near-infrared room-temperature phosphorescence of purely organic phosphors remains scarce and challenging due to strong nonradiative decay. Additionally, the investigation of triplet excimer phosphorescence is rarely reported, despite the fact that excimer, a special emitter commonly formed in crystals with strong π-π interactions, can efficiently change the fluorescent properties of compounds. Herein, a series of dithienopyrrole derivatives with low triplet energy levels and stable triplet states, exhibiting persistent near-infrared room-temperature phosphorescence, is developed. Via the modification of halogen atoms, the crystals display tunable emissions of monomers from 645 to 702 nm, with a maximum lifetime of 3.68 ms under ambient conditions. Notably, excimer phosphorescence can be switched on at low temperatures, enabled by noncovalent interactions rigidifying the matrix and stabilizing triplet excimer. Unprecedentedly, the dynamic transition process is captured between the monomer and excimer phosphorescence with temperature variations, revealing that the unstable triplet excimers in crystals with a tendency to dissociate can result in the effective quench of room-temperature phosphorescence. Excited state transitions across varying environments are elucidated, interpreting the structural dynamics of the triplet excimer and demonstrating strategies for devising novel near-infrared phosphors.

Controllable π-π coupling of intramolecular dimer models in aggregated states

π-π coupling as a common interaction plays a key role in emissions, transport and mechanical properties of organic materials. However, the precise control of π-π coupling is still challenging owing to the possible interference from other intermolecular interactions in the aggregated state, usually resulting in uncontrollable emission properties. Herein, with the rational construction of intramolecular dimer models and crystal engineering, π-π coupling can be subtly modulated by conformation variation with balanced π-π and π-solvent interactions and visualized by green-to-blue emission switching. Moreover, it can rapidly respond to temperature, pressure and mechanical force, affording a facile way to modulate π-π coupling in situ. This work contributes to a deeper understanding of the internal mechanism of molecular motions in aggregated states.

High Mobility Emissive Excimer Organic Semiconductor Towards Color-Tunable Light-Emitting Transistors

Organic light-emitting transistors (OLETs) are highly integrated and minimized optoelectronic devices with significant potential superiority in smart displays and optical communications. To realize these various applications, it is urgently needed for color-tunable emission in OLETs, but remains a great challenge as a result of the difficulty for designing organic semiconductors simultaneously integrating high carrier mobility, strong solid-state emission, and the ability for potential tunable colors. Herein, a high mobility emissive excimer organic semiconductor, 2,7-di(2-anthryl)-9H-fluorene (2,7-DAF) was reasonably designed by introducing a rotatable carbon-carbon single bond connecting two anthracene groups at the 2,7-sites of fluorene, and the small torsion angles simultaneously guarantee effective conjugation and suppress fluorescence quenching. Indeed, the unique stable dimer arrangement and herringbone packing mode of 2,7-DAF single crystal enables its superior integrated optoelectronic properties with high carrier mobility of 2.16 cm2  ⋅ V-1  ⋅ s-1 , and strong excimer emission with absolute photoluminescence quantum yield (PLQY) of 47.4 %. Furthermore, the voltage-dependent electrically induced color-tunable emission from orange to blue was also demonstrated for an individual 2,7-DAF single crystal based OLETs for the first time. This work opens the door for a new class of high mobility emissive excimer organic semiconductors, and provides a good platform for the study of color-tunable OLETs.

Highly sensitive fluorescence turn-OFF and reversible chemical sensor for Hg2+ ion based on pyrene appended 2-thiohydantoin

A novel fluorometric chemical sensor (PY-2TH) based on 2-thiohydantoin (2TH) in conjugation with pyrene (PY) was designed by facile one-pot Knoevenagel condensation reaction and explored for the sensitive and selective detection of Hg2+ ion in solution and solid state methods. Different analytical techniques like NMR and LC-MS concomitantly confirmed the structure of PY-2TH. Absorption and emission studies demonstrate positive solvatochromic effects indicating intramolecular charge transfer in polar solvents. PY-2TH exhibits unprecedented selectivity for detecting Hg2+ ions in tetrahydrofuran (THF) through turn-OFF fluorescence with 90% decrease in the emission intensity with a limit of detection (LOD) of ∼4.4 ppb. The mechanistic investigation through NMR and optical studies confirm the formation of a 2:1 complex between PY-2TH and Hg2+. Thin films of PY-2TH exhibits the J-aggregate formation in the solid state leading to a shift in the emission towards the near-infrared region. Further, we have demonstrated the applicability of PY-2TH for detection of Hg2+ ions and fluorescence imaging in live Zebrafish larvae and the toxicological effects are explored. Cytotoxic evaluation on Zebrafish larval cells revealed that PY-2TH is found to be non-toxic. Detailed analysis demonstrate the potential of PY-2TH for ultra-sensitive Hg2+ ion detection and removal in aqueous environments, highlighting its applicability for identification of metal contamination in live organisms and environmental toxicity.

Structurally Diverse Pyrene-decorated Planar Chiral [2,2]Paracyclophanes with Tunable Circularly Polarized Luminescence between Monomer and Excimer

We reported the synthesis of a series of structurally diverse CPL-active molecules, in which pyrene units were installed to chiral pm/po-[2,2]PCP scaffolds either with or without a triple bond spacer for pm/po-PCP-P1 and pm/po-PCP-P2, respectively. The X-ray crystallographic analyses revealed that these pyrene-based [2,2]PCP derivatives exhibited diverse structures and crystal packings in the solid phases. The pyrene-based [2,2]PCP derivatives exhibit various (chir)optical properties in organic solutions, depending on their respective structures. In a mixture of dioxane and water, pm/po-PCP-P1 emit green excimer fluorescence, whereas pm/po-PCP-P2 emit blue one. The chiroptical investigation demonstrated that Rp-pm-PCP-P1 and Rp-pm-PCP-P2 exhibited completely opposite CD and CPL signals even they possess the same chiral Rp-[2,2]PCP core. The same argument also holds for other chiral pyrene-based [2,2]PCP derivatives. The theoretical calculation revealed that these unusual phenomena were attributed to different orientation between transition electric dipole moments and the magnetic dipole moments originating from the presence or absence of a triple bond spacer. These pyrene-based [2,2]PCP derivatives display various colours and fluorescence emissions in the solid state and PMMA films, possibly due to the different packings as observed in the crystal structure. Moreover, these compounds also can interact with perylene diimide through π-π interactions, leading to near-white fluorescence.

4,9- and 4,10-Substituted pyrenes: synthesis, successful isolation, and optoelectronic properties

We report herein a way to prepare and purify optoelectronic functional 4,9- and 4,10-substituted pyrene isomers. By tuning the size of substituents, the designed 4,9- and 4,10-isomers can be successfully isolated by recycling preparative size-exclusion chromatography (SEC) and/or repeated recrystallization. The structure and purity of the isolated compounds 1-5 have been confirmed by 1H NMR, 13C NMR, and HRMS. The photophysical and electrochemical properties of compounds 1-5 have been studied in detail both experimentally and theoretically. The lowest transitions of these pyrenes, 1-5, are allowed, with moderate to high fluorescence quantum yields and radiative decay rates around 108 s-1. The differences between the electrochemical and photophysical properties of 4,9-, 4,10-, 1,6-, and 2,7-substituted isomers are compared and concluded.

Solvatochromism of new tetraphenylethene luminogens: integration of aggregation-induced emission and conjugation-induced rigidity for emitting strongly in both solid and solution state

In this study, we synthesized and characterized four tetraphenylethene (TPE) analogs, investigated their photophysical properties, and conducted quantum chemical calculations. Some molecules exhibited aggregation-induced emission enhancement behavior and showed efficient emission in both solid and solution states. Solvatochromism was observed in particular derivatives, with solvent polarity influencing either a bathochromic or hypsochromic shift, indicating the occurrence of photoinduced intramolecular charge transfer (ICT) processes. Quantum chemical calculations confirmed that variations in molecular packing and rigidity among the TPE analogs contributed to their diverse behavior. The study showcases aggregation in luminophores without significant impact on the excited state and highlights how minor alterations in terminal substituents can lead to unconventional behavior. These findings have implications for the development of luminescent materials. Furthermore, the synthesized compounds exhibited biocompatibility, suggesting their potential for cell imaging applications.

Enhancing Triplet-Triplet Annihilation Upconversion of Pyrene Derivatives for Photoredox Catalysis via Molecular Engineering

Triplet-triplet annihilation upconversion (TTA-UC) has the potential to enhance photoredox catalysis yield. It includes a sensitizer and an annihilator. Efficient and stable annihilators are essential for photoredox catalysis, yet only a few examples are reported. Herein, we designed four novel pyrene annihilators (1, 2, 3 and 4) via introducing aryl-alkynyl groups onto pyrene to systematically modulate their singlet and triplet energies. Coupled with platinum octaethylporphyrin (PtOEP), the TTA-UC efficiency is enhanced gradually as the number of aryl-alkynyl group increases. When combining 4 with palladium tetraphenyl-tetrabenzoporphyrin (PdTPTBP), we achieved the highest red-to-green upconversion efficiency (22.4±0.3 %) (out of a 50 % maximum) so far. Then, this pair was used to activate photooxidation of aryl boronic acid under red light (630 nm), which achieved a great improved reaction yield compared to that activated by green light directly. The results not only provide a design strategy for efficient annihilators, but also show the advantage of applying TTA-UC into improving the photoredox catalysis yield.

Highly selective Cu2+ detection with a naphthalimide-functionalised pillar[5]arene fluorescent chemosensor

Ligand 1, a rim-differentiated pillar[5]arene macrocycle modified with five naphthalimide groups through click chemistry, serves as an effective ratiometric fluorescent chemosensor for Cu2+. In contrast to the monomeric naphthalimide control compound 2, which shows only monomer emission, ligand 1 demonstrates dual emission characteristics encompassing both the monomer and excimer of the naphthalimide moieties. The binding properties of ligand 1 toward 15 different metal ions were systematically investigated in CH2Cl2/CH3CN (v/v, 1 : 1) by UV-vis and fluorescence spectroscopy. Remarkably, ligand 1 exhibits exceptional selectivity for Cu2+ ions. Upon complexation with Cu2+, the excimer emission of ligand 1 diminishes, concomitant with an enhancement of its monomer emission. The binding ratio for 1·Cu2+ was determined to be 1 : 1, with an association constant of (3.39 ± 0.40) × 105 M-1 calculated using a nonlinear least-squares curve-fitting method. Furthermore, the limit of detection (LOD) was found to be 185 ± 7 nM. Our results from 1H NMR titration, high-resolution mass spectrometry analysis and density functional theory calculations of 1·Cu2+ suggest synergistic coordination between Cu2+ and the triazole groups on ligand 1.

Highly Efficient Intramolecular Excimer Formation in a Disulfide-Linked Dipyrenyl Compound: Proton Recognition and Fluidity Assessment

Intramolecular excimer formation has been utilized extensively in chemical sciences, especially to probe solvation within complex media as well as to assess physicochemical properties of the solubilizing milieu. Pyrene has been employed extensively as a fluorescence probe for this purpose due to its favorable multidimensional fluorescence properties. Termini-capped dipyrenyl scaffolds possessing various functionalities comprise the majority of such compounds. A new both end-tagged dipyrenyl compound DTP is designed and synthesized, which exhibits significantly high intramolecular excimer formation efficiency in polar solvents. The presence of a -NH-(CO)- and/or -S-S- functionality on the chain linking the two pyrenyl groups facilitates intramolecular excimer formation. Excited-state emission intensity decay reveals that the excimer formation exclusively takes place in the excited state with only one excimer conformation. The rate constant of excimer formation is found to be higher for DTP as compared to a similar compound with an alkyl backbone. The dependence of the excimer formation on the solvent (protic versus aprotic) as well as on temperature reveals further insights into the excimer formation process. The excimer formation by DTP is found to be highly sensitive to the presence of H+: the relative excimer formation efficiency decreases drastically in the presence of a small amount of H+ (∼10-5 M). Further, the recognition of protons by DTP via intramolecular excimer formation is also observed to be highly selective in nature. Based on the observation that both the excimer formation efficiency and kinetics depend on the viscosity of the solubilizing milieu, fluidity assessment of the (dimethyl sulfoxide + acetonitrile) mixture was carried out using DTP. Further, DTP is found to be an effective probe for the assessment of the amount of water in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide as well as in a deep eutectic solvent composed of choline chloride and urea in a 1:2 mol ratio. Highly efficient and rapid intramolecular excimer formation not only establishes DTP as a useful and versatile probe but also offers strategic pathways for designing effective excimer-forming compounds.

The magic of biaryl linkers: the electronic coupling through them defines the propensity for excited-state symmetry breaking in quadrupolar acceptor-donor-acceptor fluorophores

Charge transfer (CT) is key for molecular photonics, governing the optical properties of chromophores comprising electron-rich and electron-deficient components. In photoexcited dyes with an acceptor-donor-acceptor or donor-acceptor-donor architecture, CT breaks their quadrupolar symmetry and yields dipolar structures manifesting pronounced solvatochromism. Herein, we explore the effects of electronic coupling through biaryl linkers on the excited-state symmetry breaking of such hybrid dyes composed of an electron-rich core, i.e., 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP), and pyrene substituents that can act as electron acceptors. Experimental and theoretical studies reveal that strengthening the donor-acceptor electronic coupling decreases the CT rates and the propensity for symmetry breaking. We ascribe this unexpected result to effects of electronic coupling on the CT thermodynamics, which in its turn affects the CT kinetics. In cases of intermediate electronic coupling, the pyrene-DHPP conjugates produce fluorescence spectra, spreading over the whole visible range, that in addition to the broad CT emission, show bands from the radiative deactivation of the locally excited states of the donor and the acceptors. Because the radiative deactivation of the low-lying CT states is distinctly slow, fluorescence from upper locally excited states emerge leading to the observed anti-Kasha behaviour. As a result, these dyes exhibit white fluorescence. In addition to demonstrating the multifaceted nature of the effects of electronic coupling on CT dynamics, these chromophores can act as broad-band light sources with practical importance for imaging and photonics.

Donor-Acceptor-Donor Triads with Flexible Spacers: Deciphering Complex Photophysics for Targeted Materials Design

The complex photokinetics of donor-acceptor-donor triads with varying flexible spacer lengths (n = 4-10 carbon atoms) are investigated in liquid and solid solution, as well as in crystals, by steady-state and transient fluorescence spectroscopy combined with computational studies. For the short spacer (n = 4) in a liquid solution, dynamic charge-transfer (CT) state formation with subsequent, efficient exciplex emission is observed, effectively competing with quenching through electron transfer (eT) via a radical ion pair. In a solid solution, a fluorescent CT static complex is formed upon freezing for all spacer lengths. This allows the observations of a former seminal report on stimuli-responsive high-contrast fluorescence on/off switching in films of the triads to be reassigned (Adv. Mater. 2012, 24, 5487), now providing a holistic picture on varying spacer length. In fact, external stimuli of the film by modulating the geometry of the CT complex, which results in on/off fluorescence switching (for n > 4) or in a change of the emission color (n = 4). The work thus demonstrates how in-depth analysis of complex photophysics can be put to practical use in materials science.

Development of peptide-based ratiometric fluorescent probe for sensing heparan sulfate and heparin in aqueous solutions at physiological pH and quantitative detection of heparan sulfate in live cells

Heparan sulfate (HS) plays a critical role in various biological processes as a vital component of the extracellular matrix. In this study, we synthesized three fluorescent probes (1-3) comprising Arg-rich peptides as HS receptors and a fluorophore capable of exhibiting red-shifted emissions upon aggregation. All three probes demonstrated ratiometric responses to HS and heparin in aqueous solutions. Remarkably, probe 3 exhibited a unique ratiometric response to HS in both aqueous solutions at physiological pH and HS proteoglycans on live cells. Probe 3 displayed exceptional sensing properties, including high biocompatibility, water solubility, visible light excitation, a large Stokes shift for ratiometric detection and remarkable selectivity and sensitivity for HS (with a low limit of detection: 720 pM). Binding mode studies unveiled the crucial role of charge interactions between probe 3 and negatively charged HS sugar units. Upon binding, the fluorophore segments of the probes overlapped, inducing green and red emission changes through restricted intramolecular rotation of the fluorophore moiety. Importantly, probe 3 was effectively employed to quantify the reduction of HS proteoglycan levels in live cells by inhibiting HS sulfation using siRNA and an inhibitor. It successfully detected decreased HS levels in cells treated with doxorubicin and irradiation, consistent with results obtained from western blot and immunofluorescence assays. This study presents the first ratiometric fluorescent probe capable of quantitatively detecting HS levels in aqueous solutions and live cells. The unique properties of peptide-based probe 3 make it a valuable tool for studying HS biology and potentially for diagnostic applications in various biological systems.

Supramolecular assembly of pyrene-DNA conjugates: influence of pyrene substitution pattern and implications for artificial LHCs

The supramolecular self-assembly of pyrene-DNA conjugates into nanostructures is presented. DNA functionalized with different types of pyrene isomers at the 3'-end self-assemble into nano-objects. The shape of the nanostructures is influenced by the type of pyrene isomer appended to the DNA. Multilamellar vesicles are observed with the 1,6- and 1,8-isomers, whereas conjugates of the 2,7-isomer exclusively assemble into spherical nanoparticles. Self-assembled nano-spheres obtained with the 2,7-dialkynyl pyrene isomer were used for the construction of an artificial light-harvesting complex (LHC) in combination with Cy3 as the energy acceptor.

Aggregation behaviour of pyrene-based luminescent materials, from molecular design and optical properties to application

Molecular aggregates are self-assembled from multiple molecules via weak intermolecular interactions, and new chemical and physical properties can emerge compared to their individual molecule. With the development of aggregate science, much research has focused on the study of the luminescence behaviour of aggregates rather than single molecules. Pyrene as a classical fluorophore has attracted great attention due to its diverse luminescence behavior depending on the solution state, molecular packing pattern as well as morphology, resulting in wide potential applications. For example, pyrene prefers to emit monomer emission in dilute solution but tends to form a dimer via π-π stacking in the aggregation state, resulting in red-shifted emission with quenched fluorescence and quantum yield. Over the past two decades, much effort has been devoted to developing novel pyrene-based fluorescent molecules and determining the luminescence mechanism for potential applications. Since the concept of "aggregation-induced emission (AIE)" was proposed by Tang et al. in 2001, aggregate science has been established, and the aggregated luminescence behaviour of pyrene-based materials has been extensively investigated. New pyrene-based emitters have been designed and synthesized not only to investigate the relationships between the molecular structure and properties and advanced applications but also to examine the effect of the aggregate morphology on their optical and electronic properties. Indeed, new aggregated pyrene-based molecules have emerged with unique properties, such as circularly polarized luminescence, excellent fluorescence and phosphorescence and electroluminescence, ultra-high mobility, etc. These properties are independent of their molecular constituents and allow for a number of cutting-edge technological applications, such as chemosensors, organic light-emitting diodes, organic field effect transistors, organic solar cells, Li-batteries, etc. Reviews published to-date have mainly concentrated on summarizing the molecular design and multi-functional applications of pyrene-based fluorophores, whereas the aggregation behaviour of pyrene-based luminescent materials has received very little attention. The majority of the multi-functional applications of pyrene molecules are not only closely related to their molecular structures, but also to the packing model they adopt in the aggregated state. In this review, we will summarize the intriguing optoelectronic properties of pyrene-based luminescent materials boosted by aggregation behaviour, and systematically establish the relationship between the molecular structure, aggregation states, and optoelectronic properties. This review will provide a new perspective for understanding the luminescence and electronic transition mechanism of pyrene-based materials and will facilitate further development of pyrene chemistry.

Fluorescent and Catalytic Properties of a 2D Lamellar Zn Metal-Organic Framework with sql Network Structure

A two-dimensional (2D) lamellar Zn metal-organic framework (Zn-MOF, 1) with a fluorescent 1,6-di(pyridin-3-yl)pyrene (3-DPPy) and 1,4-benzenedicarboxylate (BDC2-) bridging linkers was prepared and structurally characterized. The chemical formula of 1 is [Zn(μ-3-DPPy)(μ-BDC)]n. The mononuclear Zn(II) ion, acting as a node, is tetrahedrally coordinated with two 3-DPPy and two BDC linkers. The coordination environment of Zn(II) is a distorted tetrahedral geometry. The Zn-MOF is the sql network structure based on topology analysis. The undulated 2D sheets of 1 tightly pack together to form a lamellar structure. The pyrene moieties are parallelly oriented to each other. The Zn-MOF is not porous, possibly because the mononuclear Zn(II) node did not form cluster-based secondary building units due to the less symmetric 3-DPPy. The steady-state fluorescence measurements indicate that the fluorescence signal of the 1 is slightly blue-shifted compared to the free 3-DPPy in the solid state. The excimer emission band at 463 nm for crystalline 3-DPPy is shifted to 447 nm for 1. The value of 447 nm is also a blue-shift value compared to nonsubstituted pyrene crystals (470 nm). Despite its nonporosity, the surface Lewis acidic sites of 1 could catalyze the transesterification of esters. Surface defect sites are responsible for this catalytic activity.

Association between N-Terminal Pyrenes Stabilizes the Collagen Triple Helix

Collagen model peptides featuring the fluorophore pyrene at their N-termini have been synthesized, and their thermal denaturation has been examined using circular dichroism (CD) and fluorescence spectroscopies. Flanking the (Pro-Hyp-Gly)7 core of the peptide monomers at positions 1 and/or 23 in the primary sequence, Lys residues were introduced to ensure water solubility. Triple helices derived from such peptides show a broad excimer emission at ∼480 nm, indicative of interaction between the pyrene units. CD experiments show that the fluorophores enhance helix stability primarily through entropic effects. Unfolding temperatures (Tm) increase by up to 7 °C for systems with N-terminal lysine residues and by up to 21 °C for systems in which the first-position Lys is replaced by Ala. Tm values derived from fluorescence measurements (at 50 μM) typically lie within ∼1 °C of those obtained using CD (at 200 μM). Computational modeling in a water continuum using B3LYP-GD3 and M06-2X functionals predicts that face-to-face association of fluorophores can occur while H-bonding within the [(POG)n]3 assembly is retained. Such parallel stacking is consistent with hydrophobically driven stabilization. Labeling collagen peptides with pyrene is a synthetically simple way to promote triple helicity while providing a means to obtain Tm data on relatively dilute samples.

Organic compounds for solid state luminescence enhancement/aggregation induced emission: a theoretical perspective

Organic luminophores displaying one or more forms of luminescence enhancement in solid state are extremely promising for the development and performance optimization of functional materials essential to many modern key technologies. Yet, the effort to harness their huge potential is riddled with hurdles that ultimately come down to a limited understanding of the interactions that result in the diverse molecular environments responsible for the macroscopic response. In this context, the benefits of a theoretical framework able to provide mechanistic explanations to observations, supported by quantitative predictions of the phenomenon, are rather apparent. In this perspective, we review some of the established facts and recent developments about the current theoretical understanding of solid-state luminescence enhancement (SLE) with an accent on aggregation-induced emission (AIE). A description of the macroscopic phenomenon and the questions it raises is accompanied by a discussion of the approaches and quantum chemistry methods that are more apt to model these molecular systems with the inclusion of an accurate yet efficient simulation of the local environment. A sketch of a general framework, building from the current available knowledge, is then attempted via the analysis of a few varied SLE/AIE molecular systems from literature. A number of fundamental elements are identified offering the basis for outlining design rules for molecular architectures exhibiting SLE that involve specific structural features with the double role of modulating the optical response of the luminophores and defining the environment they experience in solid state.

Effect of Glycosylation on Self-Assembly of Lipid A Lipopolysaccharides in Aqueous Solutions

Lipopolysaccharides (LPSs) based on lipid A produced by bacteria are of interest due to their bioactivity in stimulating immune responses, as are simpler synthetic components or analogues. Here, the self-assembly in water of two monodisperse lipid A derivatives based on simplified bacterial LPS structures is examined and compared to that of a native Escherichia coli LPS using small-angle X-ray scattering and cryogenic transmission electron microscopy. The critical aggregation concentration is obtained from fluorescence probe experiments, and conformation is probed using circular dichroism spectroscopy. The E. coli LPS is found to form wormlike micelles, whereas the synthetic analogues bearing six lipid chains and with four or two saccharide head groups (Kdo₂-lipid A and monophosphoryl lipid A) self-assemble into nanosheets or vesicles, respectively. These observations are rationalized by considering the surfactant packing parameter.

New Water-Soluble Poly(propylene imine) Dendrimer Modified with 4-Sulfo-1,8-naphthalimide Units: Sensing Properties and Logic Gates Mimicking

A new water-soluble poly(propylene imine) dendrimer (PPI) modified with 4-sulfo-1,8-naphthalimid units (SNID) and its related structure monomer analog (SNIM) has been prepared by a simple synthesis. The aqueous solution of the monomer exhibited aggregation-induced emission (AIE) at 395 nm, while the dendrimer emitted at 470 nm due to an excimer formation beside the AIE at 395 nm. Fluorescence emission of the aqueous solution of either SNIM or SNID was significantly affected by traces of different miscible organic solvents, and the limits of detection were found to be less than 0.05% (v/v). Moreover, SNID exhibited the function to execute molecular size-based logic gates where it mimics XNOR and INHIBIT logic gates using water and ethanol as inputs and the AIE/excimer emissions as outputs. Hence, the concomitant execution of both XNOR and INHIBIT enables SNID to mimic digital comparators.

Polymerization-Induced Proteinosome Formation Initiated by Artificial Cells

Cellular communication is essential for living cells to coordinate the individual cellular responses and make collective behaviors. In the past decade, the communications between artificial cells have aroused great interest due to the potential applications of the structures in bioscience and biotechnology. To mimic the cellular communication, artificial cell assisted synthesis of proteinosomes was studied in this research. Multienzyme proteinosomes with glucose oxidase (GOx) and horseradish peroxidase (HRP) decorated on the membranes were synthesized by the thermally triggered self-assembly approach. Free radicals produced in a cascade reaction taking place on the surfaces of the multienzyme proteinosomes initiated reversible addition-fragmentation chain transfer (RAFT) polymerization of NIPAM at a temperature above LCST of PNIPAM in the presence of bovine serum albumin (BSA) or alcohol dehydrogenase (ADH)/acetaldehyde dehydrogenase (ALDH), and daughter proteinosomes with BSA or ADH/ALDH on the surfaces were fabricated. The structures of the GOx/HRP initiator proteinosomes, and the synthesized daughter proteinosomes were characterized with transmission electron microscopy, atomic force microscopy, fluorescence microscopy, dynamic light scattering, and micro-DSC. Enzyme activity assays demonstrate the high bioactivities of the enzymes on the surfaces of the initiator and the synthesized daughter proteinosomes.

Identification of tagged glycans with a protein nanopore

Structural complexity of glycans derived from the diversities in composition, linage, configuration, and branching considerably complicates structural analysis. Nanopore-based single-molecule sensing offers the potential to elucidate glycan structure and even sequence glycan. However, the small molecular size and low charge density of glycans have restricted direct nanopore detection of glycan. Here we show that glycan sensing can be achieved using a wild-type aerolysin nanopore by introducing a facile glycan derivatization strategy. The glycan molecule can induce impressive current blockages when moving through the nanopore after being connected with an aromatic group-containing tag (plus a carrier group for the neutral glycan). The obtained nanopore data permit the identification of glycan regio- and stereoisomers, glycans with variable monosaccharide numbers, and distinct branched glycans, either independently or with the use of machine learning methods. The presented nanopore sensing strategy for glycans paves the way towards nanopore glycan profiling and potentially sequencing.

Facile Obtainment of Fluorescent PEG Hydrogels Bearing Pyrene Groups by Frontal Polymerization

Frontal polymerization (FP) was used to prepare poly(ethylene glycol) methyl ether acrylate (PEGMA) fluorescent polymer hydrogels containing pyrenebutyl pendant groups as fluorescent probes. The polymerization procedure was carried out under solvent-free conditions, with different molar quantities of pyrenebutyl methyl ether methacrylate (PybuMA) and PEGMA, in the presence of tricaprylmethylammonium (Aliquat 336®) persulfate as a radical initiator. The obtained PEGPy hydrogels were characterized by FT-IR spectroscopy, confirming the effective incorporation of the PybuMA monomer into the polymer backbone. The thermal properties of the hydrogels were determined using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). After immersing the hydrogels in deionized water at 25 °C and pH = 7, their swelling behavior was investigated by mass gain at different pH and temperature values. The introduction of PybuMA comonomer into the hydrogel resulted in a decreased swelling ability due to the hydrophobicity of PybuMA. The optical properties of PEGPy were determined by UV-visible absorption and fluorescence spectroscopies. Both monomer and excimer emission bands were observed at 379–397 and 486 nm, respectively, and the fluorescence spectra of the PEGPy hydrogel series were recorded in different solvents to explore the coexistence of monomer and excimer emissions.

Ratiometric Fluorescence Sensing System for Lead Ions Based on Self-Assembly of Bioprobes Triggered by Specific Pb2+-Peptide Interactions

Lead is one of the most toxic substances. However, there are few ratiometric fluorescent probes for sensing Pb2+ in aqueous solution as well as living cells because specific ligands for Pb2+ ions have not been well characterized. Considering the interactions between Pb2+ and peptides, we developed ratiometric fluorescent probes for Pb2+ based on the peptide receptor in two steps. First, we synthesized fluorescent probes (1-3) based on the tetrapeptide receptor (ECEE-NH2) containing hard and soft ligands by conjugation with diverse fluorophores that showed excimer emission when they aggregated. After investigation of fluorescent responses to metal ions, benzothiazolyl-cyanovinylene was evaluated as an appropriate fluorophore for ratiometric detection of Pb2+. Next, we modified the peptide receptor to decrease the number of hard ligands and/or to replace Cys with disulfide bond and methylated Cys for improving selectivity and cell permeability. From this process, we developed two fluorescent probes (3 and 8) among the probes (1-8) that exhibited remarkable ratiometric sensing properties for Pb2+ including high water solubility (≤2% DMF), visible light excitation, high sensitivity, selectivity for Pb2+, low detection limits (<10 nM), and fast response (<6 min). The binding mode study revealed that specific Pb2+-peptide interactions of the probes caused nanosized aggregates in which the fluorophores of the probes came close each other, exhibiting excimer emission. In particular, 8 based on tetrapeptide bearing a disulfide bond and two carboxyl groups with a good permeability successfully quantified intracellular uptake of Pb2+ in live cells through ratiometric fluorescent signals. The ratiometric sensing system based on specific metal-peptide interactions and excimer emission process could provide a valuable tool to quantify Pb2+ in live cells and pure aqueous solutions.

Dipyrene-Terminated Oligosilanes Enable Ratiometric Fluorescence Response in Polymers toward Mechano- and Thermo-Stimuli

Developing fluorescent motifs capable of displaying mechano- and thermo-stimuli reversibly and ratiometrically is appealing for monitoring the deformation or temperature to which polymers are subjected. Here, a series of excimer-type chromophores Si_n-Py (n = 1-3) consisting of two pyrenes linked with oligosilanes of one to three silicon atoms is developed as the fluorescent motif incorporated in a polymer. The fluorescence of Si_n-Py is steered with the linker length where Si₂-Py and Si₃-Py with disilane and trisilane linkers display prominent excimer emission accompanied by pyrene monomer emission. Covalent incorporation of Si₂-Py and Si₃-Py in polyurethane gives fluorescent polymers PU-Si₂-Py and PU-Si₃-Py, respectively, where intramolecular pyrene excimers and corresponding combined emission of excimer and monomer are obtained. Polymer films of PU-Si₂-Py and PU-Si₃-Py display instant and reversible ratiometric fluorescence change during the uniaxial tensile test. The mechanochromic response arises from the reversible suppression of excimer formation during the mechanically induced separation of the pyrene moieties and relaxation. Furthermore, PU-Si₂-Py and PU-Si₃-Py show thermochromic response toward temperature, and the inflection point from the ratiometric emission as a function of temperature gives an indication of the glass transition temperature (T_g) of the polymers. The design of the excimer-based mechanophore with oligosilane provides a generally implementable way to develop mechano- and thermo-dual-responsive polymers.

Role of Sterically Bulky Azobenzenes in the Molecular Assembly of Pyrene Derivatives: Rectangular Sheet-like Structures and Their Emission Characteristics

The development of pyrene-based fluorescent assembled systems with desirable emission characteristics by reducing conventional concentration quenching and/or aggregation-induced quenching (ACQ) is highly desirable. In this investigation, we designed a new azobenzene-functionalized pyrene derivative (AzPy) in which sterically bulky azobenzene is linked to pyrene. Absorption and fluorescence spectroscopic results before and after molecular assembly indicate that even in a dilute N,N-dimethylformamide (DMF) solution (~10 μM), AzPy molecules experienced significant concentration quenching, whereas the emission intensities of AzPy DMF-H₂O turbid suspensions containing self-assembled aggregates were slightly enhanced and showed similar values regardless of the concentration. The shape and size of sheet-like structures, from incomplete flakes less than one micrometer in size to well-completed rectangular microstructures, could be adjusted by changing the concentration. Importantly, such sheet-like structures exhibit concentration dependence of their emission wavelength from blue to yellow-orange. Comparison with the precursor (PyOH) demonstrates that the introduction of a sterically twisted azobenzene moiety plays an important role in converting the spatial molecular arrangements from H- to J-type aggregation mode. Thus, AzPy chromophores grow into anisotropic microstructures through inclined J-type aggregation and high crystallinity, which are responsible for their unexpected emission characteristics. Our findings provide useful insight into the rational design of fluorescent assembled systems.

Molecular interaction of di-ester bonded cationic Gemini surfactants with pepsin: in vitro and in silico perspectives

The implications of surfactant-enzyme/protein interactions in a variety of fields, including biotechnology, cosmetics, paints and pharmaceuticals, have attracted a lot of attention in contemporary studies. Herein, we have employed several in vitro and in silico techniques such as excitation and absorption spectroscopies, circular dichroism and FT-IR spectroscopies, density functional and molecular dynamics simulations to understand the interaction behavior of oxy-diester-based green cationic Gemini surfactants, N1,N1,N14,N14-tetramethyl-2,13-dioxo-N1,N14-dialkyl-3,6,12-tetraoxateradecane-1,14-diaminiumdichloride (abbreviated as Cm-E2O2-Cm, where 'm' stands for alkyl chain length, m = 12 and 14) with one of the main digestive proteins, pepsin. The spectroscopic techniques confirm the static quenching effect of surfactants on pepsin. The calculated physical parameters (Ksv, Kb and ΔG) and their order reveal the distinguished implications for the surfactants' chain lengths. The spontaneity of interaction was also confirmed by negative Gibbs free energy change values. The extrinsic spectroscopic study with pyrene as fluorescence probe, FT-IR and CD techniques indicated a potential conformational change in pepsin induced by the Gemini surfactants. DFT, docking and MD simulations provided the theoretical understanding regarding the quantum mechanical environment, location of binding and stability of the protein-surfactant complexation in energy terms. We believe this study will be a humble addition to our existing knowledge in the field of protein-surfactant interactions.Communicated by Ramaswamy H. Sarma.

Monomer and Excimer Emission in a Conformational and Stacking-Adaptable Molecular System

A design strategy that combines molecular conformation, alkyl chain length, and charge-transfer effects has been developed to obtain conformational and stacking-adaptable donor-acceptor-π type molecules for precisely regulating the monomer and excimer emission in a single luminous platform under different environments. These fluorophores can exhibit bright monomer emissions when they are in the dispersed state based on their planar conformation. However, when the luminous molecules with short alkyl side chains are in the crystalline state, their molecular conformation can become distorted, further inducing strong intermolecular interactions and staggered π-π stacking for bright excimer emission. More importantly, their dispersed and aggregated states can be reversibly regulated in a phase-change fatty acid matrix, to achieve temperature-responsive fluorescence for temperature monitoring and advanced information encryption.

Self-healing cyclic peptide hydrogels

Hydrogels are soft materials of great interest in different areas such as chemistry, biology, and therapy. Gels made by the self-assembly of small molecules are known as supramolecular gels. The modulation of their properties by monomer molecular design is still difficult to predict due to the potential impact of subtle structural modifications in the self-assembly process. Herein, we introduce the design principles of a new family of self-assembling cyclic octapeptides of alternating chirality that can be used as scaffolds for the development of self-healing hydrogelator libraries with tunable properties. The strategy was used in the preparation of an amphiphilic cyclic peptide monomer bearing an alkoxyamine connector, which allowed the insertion of different aromatic aldehyde pendants to modulate the hydrophobic/hydrophilic balance and fine-tune the properties of the resulting gel. The resulting amphiphiles were able to form self-healable hydrogels with viscoelastic properties (loss tangent, storage modulus), which were strongly dependent on the nature and number of aromatic moieties anchored to the hydrophilic peptide. Structural studies by SEM, STEM and AFM indicated that the structure of the hydrogels was based on a dense network of peptide nanotubes. Excellent agreement was established between the peptide primary structure, nanotube length distributions and viscoelastic behaviour.

Tricyclic octaurea "Temples" for the recognition of polar molecules in water

Two water-soluble tricyclic "Temple" macrocycles featuring pyrene roof/floor units and bis-urea spacers have been synthesised and studied as receptors for aromatic compounds in aqueous media. The tricycles show good selectivity for methylated purine alkaloids such as caffeine versus unsubstituted heterocycles such as adenine and indole. Binding is signalled by major changes in fluorescence, apparently due to the break-up of intramolecular excimers. The formation of excimers implies cavity collapse in the absence of guests explaining why, unlike an earlier relative, these receptors do not bind carbohydrates. Naphthalenediimides (NDIs) have also been studied as geometrically complementary guests, and indeed bind especially strongly (K_a > 10⁷ M^-1); this powerful and selective association suggests potential applications in supramolecular self-assembly.

Luminescent Complexes of Platinum, Iridium, and Coinage Metals Containing N-Heterocyclic Carbene Ligands: Design, Structural Diversity, and Photophysical Properties

The employment of N-heterocyclic carbenes (NHCs) to design luminescent metal compounds has been the focus of recent intense investigations because of the strong σ-donor properties, which bring stability to the whole system and tend to push the d-d dark states so high in energy that they are rendered thermally inaccessible, thereby generating highly emissive complexes for useful applications such as organic light-emitting diodes (OLEDs), or featuring chiroptical properties, a field that is still in its infancy. Among the NHC complexes, those containing organic chromophores such as naphthalimide, pyrene, and carbazole exhibit rich emission behavior and thus have attracted extensive interest in the past five years, especially carbene coinage metal complexes with carbazolate ligands. In this review, the design strategies of NHC-based luminescent platinum and iridium complexes with large spin-orbit-coupling (SOC) are described first. Subsequent paragraphs illustrate the recent advances of luminescent coinage metal complexes with nucleophilic- and electrophilic-based carbenes based on silver, gold, and copper metal complexes that have the ability to display rich excited state emissions in particular via thermally activated delayed fluorescence (TADF). The luminescence mechanism and excited state dynamics are also described. We then summarize the advance of NHC-metal complexes in the aforementioned fields in recent years. Finally, we propose the development trend of this fast-growing field of luminescent NHC-metal complexes.

Ratiometric detection of polymyxin B based on the disaggregation of pyrenyl nanoassemblies in 100% aqueous media

Polymyxin B (PMB) was an antibiotic with highly effective antibacterial effect but narrow safety interval, and its residues in food had attracted widespread attention. It was important to develop an accurate method for the rapid detection of PMB in animal foods. In this work, we had established a ratiometric sensing system based on the formation of supramolecular assemblies of pyrenyl probes, which were driven by the synergy of noncovalent forces such as multiple-electrostatic and π-π stacking interactions. Compared with the traditional fluorescence detection based on the single wavelength change, the present approach showing two-wavelength fluorescence response could reduce the interference of other factors making the experimental results more accurate. The sensor exhibited high sensitivity and selectivity with a low detection limit (28.3 nM). This method could be used to realize visual detection and had a visual detection limit of 1 μM. As we had learned yet, this was the first ratiometric sensor for PMB detection in aqueous solution. We believed all our preliminary would not only provide a complementary strategy for the detection of PMB, but also develop some new ideas for the construction of sensors for rapid antibiotic detection.

Double Stimuli-Responsive di- and Triblock Copolymers of Poly(N-isopropylacrylamide) and Poly(1-vinylimidazole): Synthesis and Self-Assembly

For the first time, double stimuli-responsive properties of poly(N-isopropylacrylamide) (PNIPA) and poly(1-vinylimidazole) (PVIM) block copolymers in aqueous solutions were studied. The synthesis of PNIPA₆₀-b-PVIM₉₀ and PNIPA₂₈-b-PVIM₆₂-b-PNIPA₂₉ was performed using reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymers were characterized by size exclusion chromatography and ¹H NMR spectroscopy. The conformational behavior of the polymers was studied using dynamic light scattering (DLS) and fluorescence spectroscopy (FS). It was found that PNIPA and block copolymers conformation and ability for self-assembly in aqueous medium below and above cloud point temperature depend on the locus of hydrophobic groups derived from the RAFT agent within the chain. Additionally, the length of PVIM block, its locus in the chain and charge perform an important role in the stabilization of macromolecular micelles and aggregates below and above cloud point temperature. At 25 °C the average hydrodynamic radius (R_h) of the block copolymer particles at pH 3 is lower than at pH 9 implying the self-assembling of macromolecules in the latter case. Cloud points of PNIPA₆₀-b-PVIM₉₀ are ~43 °C and ~37 °C at a pH of 3 and 9 and of PNIPA₂₈-b-PVIM₆₂-b-PNIPA₂₉ they are ~35 °C and 31 °C at a pH of 3 and 9. Around cloud point independently of pH, the R_h value for triblock copolymer rises sharply, achieves the maximum value, then falls and reaches the constant value, while for diblock copolymer, it steadily grows after reaching cloud point. The information about polarity of microenvironment around polymer obtained by FS accords with DLS data.

Analyte Detection: A Decade of Progress in the Development of Optical/Fluorescent Sensing Probes

The development of selective and sensitive chemical sensors capable of detecting metal ions, anions, neutral species, explosives and hazardous substances, selectively and sensitively has attracted considerable interest of various research groups. The presence of such analytes within the permissible limits is often beneficial, but the excess amounts may lead to lethal effects to both the environment as well as the living organisms. Owing to the toxicity of the heavy metal ions, toxic anions and nitro-aromatics which are main constituents of explosives, the timely detection of these materials is most desirable to ensure safety and security of the mankind. In this personal account, we present several classes of molecular sensors that were specifically designed in our lab during the past decade for detecting several species in solutions, solid state as well as biological media. Modulation of the optical properties in response to the presence of guest species, led to selective and sensitive detection protocols, and was supported by the theoretical studies wherever possible. We have also extended the application of some of these probes for the on-site detection of analytes by developing the paper strips, glass slides and even the wool and cotton fabrics loaded with probes. One such development represents detection of palladium in human urine and blood samples collected from clinical samples. Additionally, the sensing events in some cases have successfully been reproduced in the live cancer cells. Based on the ease and cost-effective synthesis of the molecular probes, we hope that this account shall provide significant information to researchers in understanding the structure dependent sensing capabilities of the molecular probes.

Selective and Reversible Solvent Uptake in Tetra-4-(4-pyridyl)phenylmethane-based Supramolecular Organic Frameworks

The dynamic behavior of supramolecular organic frameworks (SOFs) based on the rigid tetra-4-(4-pyridyl)phenylmethane (TPPM) organic tecton has been elucidated through 3D electron diffraction, X-ray powder diffraction and differential scanning calorimetry (DSC) analysis. The SOF undergoes a reversible single-crystal-to-single-crystal transformation when exposed to vapours of selected organic solvents, moving from a closed structure with isolated small voids to an expanded structure with solvated channels along the b axis. The observed selectivity is dictated by the fitting of the guest in the expanded SOF, following the degree of packing coefficient. The effect of solvent uptake on TPPM solid-state fluorescence was investigated, evidencing a significant variation in the emission profile only in the presence of chloroform.

Recent Advances in Excimer-Based Fluorescence Probes for Biological Applications

The fluorescent probe is a powerful tool for biological sensing and optical imaging, which can directly display analytes at the molecular level. It provides not only direct visualization of biological structures and processes, but also the capability of drug delivery systems regarding the target therapy. Conventional fluorescent probes are mainly based on monomer emission which has two distinguishing shortcomings in practice: small Stokes shifts and short lifetimes. Compared with monomer-based emission, excimer-based fluorescent probes have large Stokes shifts and long lifetimes which benefit biological applications. Recent progress in excimer-based fluorescent sensors (organic small molecules only) for biological applications are highlighted in this review, including materials and mechanisms as well as their representative applications. The progress suggests that excimer-based fluorescent probes have advantages and potential for bioanalytical applications.

Full-Color and Switchable Circularly Polarized Light from a Macroscopic Chiral Dendritic Film through a Solid-State Supramolecular Assembly

Chiral materials displaying chirality across multiple length scales have attracted increasing interest due to their potential applications in diverse fields. Herein, we report an efficient approach for the construction of macroscopic crystal dendrites with hierarchical chirality based on an in situ solid assembly in a block copolymer film. Chiral fluorescent crystals are formed by enantiopure d-/l-dibenzoyl tartaric acid and pyrenecarboxylic acid in a poly(1,4-butadiene)-b-poly(ethylene oxide) film. The chiro-optical activity of the crystalline dendrites can be greatly amplified in the absorption and scattering regions and goes along with the dimension of dendrites. Notably, the chiral dendrites exhibited strong circularly polarized luminescence emission with a high dissymmetric factor (0.03). The enhancement of the quantum yield of the chiral film was up to 28%, which was 14 times higher that of the corresponding fluorescent molecules. The circularly polarized emission bands of the films can be fine-tuned by contriving the emissive bands of fluorescent molecules. More importantly, the chiral signals are able to be wiped when the fluorescent group photodimerizes under UV irradiation. This work provides an efficient way to develop functional materials through solid self-assembly.

A Peptide-Based Hydrogel for Adsorption of Dyes and Pharmaceuticals in Water Remediation

The removal of dyes and pharmaceuticals from water has become a major issue in recent years due to the shortage of freshwater resources. The adsorption of these pollutants through nontoxic, easy-to-make, and environmentally friendly adsorbents has become a popular topic. In this work, a tetrapeptide-pyrene conjugate was rationally designed to form hydrogels under controlled acidic conditions. The hydrogels were thoroughly characterized, and their performance in the adsorption of various dyes and pharmaceuticals from water was investigated. The supramolecular hydrogel efficiently adsorbed methylene blue (MB) and diclofenac (DCF) from water. The effect of concentration in the adsorption efficiency was studied, and results indicated that while the adsorption of MB is governed by the availability of adsorption sites, in the case of DCF, concentration is the driving force of the process. In the case of MB, the nature of the dye-hydrogel interactions and the mechanism of the adsorption process were investigated through UV-Vis absorption spectroscopy. The studies proved how this dye is first adsorbed as a monomer, probably through electrostatic interactions; successively, at increasing concentrations as the electrostatic adsorption sites are depleted, dimerization on the hydrogel surface occurs.

Combined experimental and TD-DFT/DMOl3 investigations, optical properties, and photoluminescence behavior of a thiazolopyrimidine derivative

We present here the FT-IR, DFT computation, XRD, optical, and photophysical characterization of a heterocyclic compound with thienopyrimidine and pyran moieties. TD-DFT/DMOl³ and TD-DFT/CASTEP computations were used to study the geometry of isolated and dimer molecules and their optical behavior. The indirect (3.93 eV) and direct (3.29 eV) optical energy bandgaps, HOMO-LUMO energy gap (3.02 eV), and wavelength of maximum absorption (353 nm) were determined in the gas phase with M062X/6-31+G (d, p). A thin film of the studied molecule was studied using XRD, FT-IR, and UV-Vis spectroscopy. The average crystallite size was found as 74.95 nm. Also, the photoluminescence spectroscopy revealed that the compound exhibited different emission bands at the visible range with different intensities depending on the degree of molecular aggregation. For instance, solutions with different concentrations emitted blue, cyan, and green light. On the other hand, the solid-state material produced a dual emission with comparable intensities at λ_max = 455, 505, and 621 nm to cover the entire visible range and produce white emission from a single material with CIE coordinates of (0.34, 0.32) that are very similar to the ideal pure white light. Consequently, these findings could lead to the development of more attractive new luminous materials.