Amorphous 2‑Bromocarbazole Copolymers with Efficient Room-Temperature Phosphorescent Emission and Applications as Encryption Ink

The development of metal-free organic room-temperature phosphorescent (RTP) materials is promising but challenging, because spin–orbit coupling is less efficient without heavy metals such as platinum and palladium. Here, we present a novel amorphous copolymer composed of 2-bromocarbazole phosphor and acrylamide on its side chains, which can engender blue–purple phosphorescence emission with high quantum yield at room temperature. The polymer matrices of acrylamide and the hydrogen bonding in the polymeric chain system can effectively help to inhibit nonradiative transition process and, hence, strengthen the phosphorescent emission. The molar ratio of the 2-bromocarbazole phosphor and acrylamide remarkably influences the RTP emission intensities and quantum yields of the polymers. The high amount of phosphor will weaken the rigidity of the polymers and the shielding effect from oxygen, thus leading to a decrease in their RTP emission, while a low concentration of the phosphor will also weaken their RTP emission intensity. Furthermore, RTP intensity of the amorphous polymer is responsive to humidity, because the hydrogen bonding in the polymeric chain system can be broken by water, which makes it applicable in the area of encryption

Taking Orders from Light: Photo-Switchable Working/Inactive Smart Surfaces for Protein and Cell Adhesion

Photoresponsive smart surfaces are promising candidates for a variety of applications in optoelectronics and sensing devices. The use of light as an order signal provides advantages of remote and noninvasive control with high temporal and spatial resolutions. Modification of the photoswitches with target biomacromolecules, such as peptides, DNA, and small molecules including folic acid derivatives and sugars, has recently become a popular strategy to empower the smart surfaces with an improved detection efficiency and specificity. Herein, we report the construction of photoswitchable self-assembled monolayers (SAMs) based on sugar (galactose/mannose)-decorated azobenzene derivatives and determine their photoswitchable, selective protein/cell adhesion performances via electrochemistry. Under alternate UV/vis irradiation, interconvertible high/low recognition and binding affinity toward selective lectins (proteins that recognize sugars) and cells that highly express sugar receptors are achieved. Furthermore, the <i>cis</i>-SAMs with a low binding affinity toward selective proteins and cells also exhibit minimal response toward unselective protein and cell samples, which offers the possibility in avoiding unwanted contamination and consumption of probes prior to functioning for practical applications. Besides, the electrochemical technique used facilitates the development of portable devices based on the smart surfaces for on-demand disease diagnosis

Multicolor Photoluminescence of a Hybrid Film via the Dual-Emitting Strategy of an Inorganic Fluorescent Au Nanocluster and an Organic Room-Temperature Phosphorescent Copolymer

Achieving multicolor photoluminescence, especially white-light emission, under mild conditions based on hybrid organic–inorganic materials has attracted growing attention. A novel system, via a histidine modified Au nanocluster (AuNC@histidine) with bluish green fluorescence and a 4-bromo-1,8-naphthalic anhydride derivative polymer (poly-BrNpA) with orange room-temperature phosphorescence (RTP) emission, was designed and prepared. White-light emission could be achieved by adjusting the proportions of the two components. The hydrogen bond enhanced the RTP emission of such copolymer systems through suppressing the nonradiative relaxation process by the well-formed and highly cross-linked network. By introducing fluorescence compounds (AuNC@histidine) which were insensitive to environmental humidity, this fluorescence-phosphorescence dual-emitting hybrid system could also be used as a humidity responsive material, since the hydrogen bonds in poly-BrNpA chains could be broken by environmental humidity. The color switching could be well conducted in a poly­(vinyl alcohol) (PVA) matrix, which was good for forming a processable and humidity responsive film

D-A-π-A Featured Sensitizers Bearing Phthalimide and Benzotriazole as Auxiliary Acceptor: Effect on Absorption and Charge Recombination Dynamics in Dye-Sensitized Solar Cells

Two organic D-A-π-A sensitizers <b>LS-2</b> and <b>WS-5</b> containing <i>N</i>-octyl substituted phthalimide and benzotriazole as auxiliary electron withdrawing units with similar dimension and structure architecture were systematically studied, focusing on photophysical and electrochemical as well as photovoltaic properties in nanocrystalline TiO₂-based dye-sensitized solar cells (DSSCs). Interestingly, with similar five-member benzo-heterocycles, the two auxiliary acceptors of phthalimide and benzotriazole play exactly different roles in absorption and intramolecular charge transfer: (i) in contrast with <b>WS-5</b> delocalized throughout the entire chromophore, the HOMO orbital of <b>LS-2</b> is mainly located at the donor part due to the twist conformation with the existence of two carbonyl groups in phthalimide; (ii) the dihedral angles of “D-A” plane and “A-π” plane in <b>LS-2</b> further suggest that the incorporation of phthalimide moiety results in curvature of electron delocalization over the whole molecule, in agreement with its blue-shifted, relatively narrow absorption spectra and low photocurrent density; (iii) in contrast with the beneficial charge transfer of benzotriazole in <b>WS-5</b>, the phthalimide unit in <b>LS-2</b> plays an oppositely negative contribution to the charge transfer, that is, blocking intramolecular electron transfer (ICT) from donor to acceptor to some extent; and (iv) in electrochemical impedance spectroscopy, the incorporated benzotriazole unit enhances electron lifetime by 18.6-fold, the phthalimide only increases electron lifetime by 5.0-fold. Without coadsorption of chenodeoxylic acid (CDCA), the DSSCs based on <b>WS-5</b> exhibited a promising maximum conversion efficiency (η) of 8.38% with significant enhancement in all photovoltaic parameters (<i>J</i>_SC = 15.79 mA cm^–2, <i>V</i>_OC = 791 mV, <i>ff</i> = 0.67). In contrast, with the very similar D-A-π-A feature changing the additional acceptor from benzotriazole to phthalimide unit, the photovoltaic efficiency based on <b>LS-2</b> was only 5.11%, decreased by 39%, with less efficient photovoltaic parameters (<i>J</i>_SC = 10.06 mA cm^–2, <i>V</i>_OC = 748 mV, <i>ff</i> = 0.68). Therefore, our results demonstrate that it is essential to choose proper subsidiary withdrawing unit in D-A-π-A sensitizer configuration for DSSCs

Pyrimidine-2-carboxylic Acid as an Electron-Accepting and Anchoring Group for Dye-Sensitized Solar Cells

We report a new dye (INPA) adopting pyrimidine-2-carboxylic acid as an electron-accepting and anchoring group to be used in dye-sensitized solar cells. IR spectral analysis indicates that the anchoring group may form two coordination bonds with TiO₂ and so facilitate the interaction between the anchoring group and TiO₂. The INPA-based cell exhibits an overall conversion efficiency of 5.45%, which is considerably higher than that obtained with cyanoacrylic acid commonly used as the electron acceptor

Optimizing the Chemical Recognition Process of a Fluorescent Chemosensor for α‑Ketoglutarate

α-Ketoglutarate (α-KA) can convert to 2-hydroxyglutarate (2-HG), which is confirmed to be associated with many diseases, especially with acute myeloid leukemia (AML). In this paper, a novel reaction-based chemosensor DT based on the typical Schiff-base reaction was designed for sensing the biomarker of α-KA, in which a diazanyl group as the recognition group was linked with a benzothiadiazole unit as the fluorophore moiety. Considering the typical Schiff-base reaction to generate hydrazones suffering from slow kinetics, particularly under neutral conditions, a series of parallel experiments was conducted for optimizing the chemical recognition process, including varying the solvent, reaction temperature, reactant concentration, and reaction rate. The optimum condition was established as a pH value, temperature, α-KA concentration, and response time of 5.7, 30 °C, 100 μM, and 20 min, respectively. Notably, in contrast with the initial 6.3-fold fluorescence enhancement, the remarkable 75-fold fluorescence enhancement ((<i>I</i> – <i>I</i>₀)/<i>I</i>₀ at 560 nm) was observed by optimizing the chemical recognition process of DT and α-KA. Finally, DT was carried out for the chemical recognition processing of α-KA in serum. We demonstrated that DT is selective for α-KA over other potential biologically interferences with similar structures and thus is suitable for detecting α-KA in serum. On the basis of the optimized chemical recognition process, DT shows high potential application for sensing α-KA with remarkable fluorescence enhancement. This work provided a potential method that is quick and convenient for sensing biomarker α-KA in serum. It is worth noting that without complicated pretreatment, utilizing a novel reaction-based fluorescent chemosensor may establish a new promising platform for clinical diagnosis biomarker

Bis‑<i>p</i>‑Sulfonatocalix[4]arene-Based Supramolecular Amphiphiles with an Emergent Lower Critical Solution Temperature Behavior in Aqueous Solution and Hydrogel

An unexpected lower critical solution temperature (LCST) phenomenon is observed in a <i>bis</i>-<i>p</i>-sulfonatocalix­[4]­arene-based supramolecular amphiphile system, and the mechanism of this intriguing phenomenon is studied. The unusual macroscopic thermoresponsive behavior is based on the switch of the system from water-soluble assemblies to insoluble netlike cross-linked nanoparticles under temperature stimulus, which is regulated by multiple weak interactions, including hydrophilic and hydrophobic interactions, π–π stacking, and host–guest recognition. By using the LCST solution as the dispersion medium, a hydrogel with LCST behavior can be fabricated. This work contributes toward better understanding about calixarene-induced aggregation (CIA) and thermoresponsive self-assembled systems. It will also help to enrich the designing of complexed supramolecular amphiphile systems and develop their potential applications in hydrogels

Synthesis, characterization, and magnetochemical properties of two Mn₄ clusters derived from 2-pyridinecarboxaldehyde Schiff base ligands

<p>Two tetranuclear manganese complexes, [Mn₄(L¹)₆](ClO₄)₂⋅2.75H₂O (<b>1</b>) [HL¹ = 4-methyl-2-((pyridin-2-ylmethylene)amino)phenol] and [Mn₄(L²)₄(NO₃)₃(OH)]⋅pz⋅3H₂O (<b>2</b>) [HL² = (1<i>H</i>-pyrazol-1-yl)(pyridin-2-yl)methanol, pz = pyrazole], have been synthesized and characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction, and magnetic measurements. The structural analysis revealed that the central manganese ion is linked with three apical manganese ions through six phenoxo-bridges creating a Mn₄O₆ core for <b>1</b>; <b>2</b> has a cubane-like topology with the Mn(II) ions and the deprotonated oxygens from L² alternatively occupying vertices. The magnetic studies indicated a weak ferromagnetic coupling interaction (<i>J</i> = 0.48 ± 0.087 cm⁻¹, <i>g</i> = 2.00, <i>θ</i> = −0.78 K) for <b>1</b> and a weak antiferromagnetic spin-exchange interaction (<i>J</i>₁ = −0.50 ± 0.075 cm⁻¹, <i>J</i>₂ = −0.13 ± 0.082 cm⁻¹, <i>g</i> = 1.98) between Mn(II) ions for <b>2</b>. The magnetostructural correlations of the two Mn₄ clusters have been discussed tentatively.</p

Photocontrolled Fluorescence “Double-Check” Bioimaging Enabled by a Glycoprobe–Protein Hybrid

Despite the rapid development of imaging techniques, precise probe localization and modulation in living cells is still a challenging task. Here we show that the simple hybridization between a photochromic fluorescent glycoprobe and human serum albumin (HSA) enables a unique fluorescence “double-check” mechanism for precisely localizing and manipulating probe molecules in living cells. Docking of a carbohydrate-modified naphthalimide (Naph)-spiropyran (SP) dyad to a hydrophobic pocket of HSA produces the glycoprobe-protein hybrid, causing the protein conformation to fold as determined by small-angle X-ray scattering. We show that the Naph and merocyanine (the photoisomer of SP) fluorescence of the resulting hybrid can be reversibly switched by light in buffer solution and in target cells overexpressing the carbohydrate receptor

A Ferrocene-Functionalized [2]Rotaxane with Two Fluorophores as Stoppers

In the past few decades, bistable [2]­rotaxanes have been extensively studied because of their applications in the fields of functional molecules and molecular machines. In this paper, a di-ferrocene-functionalized [2]­rotaxane with two fluorophores as stoppers was designed, prepared, and studied. In this bistable [2]­rotaxane, a dibenzo-24-crown-8 macrocycle functionalized with two ferrocene moieties as electron donors can reversibly shuttle between two distinct stations, namely, a dialkylammonium recognition site and a <i>N</i>-methyltriazolium recognition site, by external acid–base stimuli, which has been demonstrated using ¹H NMR spectroscopy. It has been shown that, by introducing two ferrocene units into the macrocycle component, the fluorescence of two fluorescent stoppers, namely, the anthracene fluorophore and the 4-morpholin-naphthalimide fluorophore, can be changed in an alternate mode by an adjustable, distance-dependent photoinduced electron transfer process that occurs between the ferrocene electron donors and each of the two fluorophores