Controlling the Emergence and Shift Direction of Mechanochromic Luminescence Color of a Pyridine‐Terminated Compound

In this study, mechanochromic luminescence was induced in a complex of mechano‐inactive compounds. Dye/acid complexes containing the same π‐conjugated backbones were prepared. While the luminophore showed blue and red shifts in photoluminescence spectra when combined with different acids by grinding, it exhibited slight mechanoresponsiveness itself. Also, compounds with similar molecular backbones to the dye/acid complex were synthesized to clarify the color change mechanism. The compounds showed both blue and red shifts in photoluminescence and diffuse reflectance spectra upon grinding, indicating that mechanochromic luminescence in the hydrogen‐bonded complex is like its monomeric analogue and that aggregation structure plays an important role in mechanoresponsive behavior rather than the π‐conjugated structure. It was shown that a color change can be mechanically induced by imitating the solid‐state aggregation structure of other mechanoresponsive compounds without synthetic modification.     

Computational Design,Synthesis, and Mechanochromic Properties of New Thiophene‐Based π‐Conjugated Chromophores

The possibility of exploiting supramolecular architectures for the preparation of innovative mechanochromic devices has been extended by designing novel thienyl‐substituted 1,4‐bis(ethynyl)benzene dyes, which are characterized by a conjugated, rigid, rodlike core structure. This new family of chromophores was synthesized according to a simple two‐step sequential cross‐coupling reaction, and the optical properties were investigated in solution and in a polymeric matrix. To tune the mechanochromic performances in smart polymer materials, a virtual screening was set up that was able to select a derivative with optimal spectral features. The effective combination of experimental and computational investigations allowed us to spot those homologues with already potential anisotropic and aggregachromic features and characterized by the best spectral properties and luminescent response. The best candidate was synthesized and dispersed into a polyethylene matrix, indeed achieving an “in silico designed” mechanochromic material. Besides the specific applications of this novel material, the integration of computational and experimental techniques reported here defines an efficient protocol that can be applied to make a selection among similar dye candidates, which constitute the essential responsive part of such supramolecular devices.     

All‐Solid‐State Ion Selective and All‐Solid‐State Reference Electrodes

This paper is aiming to give a brief overview of recent research in the field of all‐solid‐state, internal solution free, ion‐selective electrodes and reference electrodes, employing conducting polymers or nano‐/microstructures as solid contacts beneath the polymeric, ion‐selective or reference membranes. The emphasis is on papers published in the last five years (after 2006). According to the papers published, poly(3‐octylthiophene) conducting polymer transducers offer highly reliable sensors for various applications, involving demanding analytical approaches and miniature sensors. On the other hand, the search for alternative materials continues: the sensors obtained by placing nano‐/microstructures (conducting polymers but also other materials, like, e.g., carbon nanotubes) underneath the receptor membrane are intensively tested. The recent years have also shown how useful the application of advanced instrumental methods is for the investigation of processes occurring within all‐solid‐state ion‐selective electrodes.     

Luminescence Color‐Tuning through Polymorph Doping: Preparation of a White‐Emitting Solid from a Single Gold(I)–Isocyanide Complex by Simple Precipitation

We report the luminescent color tuning of a new complex, 2‐benzothiophenyl(4‐methoxyphenyl isocyanide)gold(I) ( 1 ), by using a new “polymorph doping” approach. The slow crystallization of the complex 1 afforded three different pure polymorphic crystals with blue, green, and orange emission under UV‐light irradiation. The crystal structures of pure polymorphs of 1 were investigated in detail by means of single‐crystal X‐ray analyses. Theoretical calculations based on the single‐crystal structures provided qualitative explanation of the difference in the excited energy‐levels of the three polymorphs of 1 . In sharp contrast, the rapid precipitation of 1 , with the optimized conditions reproducibly afforded homogeneous powder materials showing solid‐state white‐emission with Commission Internationale de l’Éclairage (CIE) 1931 chromaticity coordinates of (0.33, 0.35), which is similar to pure white. New “polymorphic doping” has been revealed to be critical to this white emission through spectroscopic and X‐ray diffraction analyses. The coexistence of the multiple polymorphs of 1 within the homogeneous powder materials and the ideal mixing of multiple luminescent colors gave its white emission accompanied with energy transfer from the predominant green‐emitting polymorph to the minor orange‐emitting polymorph.     

2,2′‐Bipyrimidine as Efficient Sensitizer of the Solid‐State Luminescence of Lanthanide and Uranyl Ions from Visible to Near‐Infrared

Treatment of Ln(NO₃)₃?nH₂O with 1 or 2 equiv 2,2′‐bipyrimidine (BPM) in dry THF readily afforded the monometallic complexes [Ln(NO₃)₃(bpm)₂] (Ln=Eu, Gd, Dy, Tm) or [Ln(NO₃)₃(bpm)₂]?THF (Ln=Eu, Tb, Er, Yb) after recrystallization from MeOH or THF, respectively. Reactions with nitrate salts of the larger lanthanide ions (Ln=Ce, Nd, Sm) yielded one of two distinct monometallic complexes, depending on the recrystallization solvent: [Ln(NO₃)₃(bpm)₂]?THF (Ln=Nd, Sm) from THF, or [Ln(NO₃)₃(bpm)(MeOH)₂]?MeOH (Ln=Ce, Nd, Sm) from MeOH. Treatment of UO₂(NO₃)₂?6H₂O with 1 equiv BPM in THF afforded the monoadduct [UO₂(NO₃)₂(bpm)] after recrystallization from MeOH. The complexes were characterized by their crystal structure. Solid‐state luminescence measurements on these monometallic complexes showed that BPM is an efficient sensitizer of the luminescence of both the lanthanide and the uranyl ions emitting visible light, as well as of the Yb^III ion emitting in the near‐IR. For Tb, Dy, Eu, and Yb complexes, energy transfer was quite efficient, resulting in quantum yields of 80.0, 5.1, 70.0, and 0.8 %, respectively. All these complexes in the solid state were stable in air.     

All‐Solid‐State Chloride Sensors with Poly(3‐Octylthiopene) Matrix and Trihexadecylmethylammonium Chlorides as an Ion Exchanger Salt

All‐solid‐state chloride sensors were prepared by incorporation of trihexadecyl‐methylammonium chloride (THMACl) as an ion‐exchanger salt into a conjugated polymer membrane, poly(3‐octylthiophene) (POT). The influence of additional membrane components, such as a lipophilic anion, (potassium tetrakis[3,5‐bis(trifluoromethyl)phenyl] borate), poly(vinyl chloride) (PVC) or a plasticizer, (2‐nitrophenyl octyl ether) were studied. The membrane components were dissolved in chloroform except for PVC, which was dissolved in tetrahydrofuran (THF). The membrane solution was deposited on glassy carbon (GC) by solution casting resulting in all‐solid‐state chloride sensors. The sensor characteristics were determined potentiometrically and with impedance spectroscopy. The addition of plasticizer was found to be crucial in obtaining a well functioning Cl^?‐ISE based on POT and THMACl.     

Single‐Crystal‐to‐Single‐Crystal Transformation and Solvochromic Luminescence of a Dinuclear Gold(I)–(Aza‐[18]crown‐6)dithiocarbamate Compound

The treatment of [AuCl(SMe₂)] with an equimolar amount of NaO₅NCS₂ (O₅NCS₂=(aza‐[18]crown‐6)dithiocarbamate) in CH₃CN gave [Au₂(O₅NCS₂)₂] ? 2 CH₃CN ( 2? 2 CH₃CN), and its crystal structure displays a dinuclear gold(I)‐azacrown ether ring and an intermolecular gold(I) ??? gold(I) contact of 2.8355(3) Å in crystal lattices. It is noted that two other single crystals of 2 ?tert‐butylbenzene?H₂O and 2? 0.5 m‐xylene can be successfully obtained from a single‐crystal‐to‐single‐crystal (SCSC) transformation process by immersing single crystals of 2? 2 CH₃CN in the respective solvents, and both also show intermolecular gold(I) ??? gold(I) contacts of 2.9420(5) and 2.890(2)–2.902(2) Å, respectively. Significantly, the emissions of all three 2 ?solvates are well correlated with their respective intermolecular gold(I) ??? gold(I) contacts, where such contacts increase with 2? 2 CH₃CN (2.8355(3) Å)< 2? 0.5 m‐xylene (2.890(2)–2.902(2) Å)< 2? tert‐butylbenzene?H₂O (2.9420(5) Å), and their emission energies increase with 2? 2 CH₃CN (602 nm)< 2? 0.5 m‐xylene (583 nm)< 2? tert‐butylbenzene?H₂O (546 nm) as well. In this regard, we further examine the solvochromic luminescence for some other aromatics, and finally their emissions are within 546–602 nm. Obviously, the above results are mostly ascribed to the occurrence of intermolecular gold(I) ??? gold(I) contacts in 2 ?solvates, which are induced by the presence of various solvates in the solid state, as a key role to be responsible for their solvochromic luminescence.     

Polymorph‐Dependent Solid‐State Fluorescence and Selective Metal‐Ion‐Sensor Properties of 2‐(2‐Hydroxyphenyl)‐4(3H)‐quinazolinone

2‐(2‐Hydroxy‐phenyl)‐4(3H)‐quinazolinone (HPQ), an organic fluorescent material that exhibits fluorescence by the excited‐state intramolecular proton‐transfer (ESIPT) mechanism, forms two different polymorphs in tetrahydrofuran. The conformational twist between the phenyl and quinazolinone rings of HPQ leads to different molecular packing in the solid state, giving structures that show solid‐state fluorescence at 497 and 511 nm. HPQ also shows intense fluorescence in dimethyl formamide (DMF) solution and selectively detects Zn²⁺ and Cd²⁺ ions at micromolar concentrations in DMF. Importantly, HPQ not only detects Zn²⁺ and Cd²⁺ ions selectively, but it also distinguishes between the metal ions with a fluorescence λ_max that is blue‐shifted from 497 to 420 and 426 nm for Zn²⁺ and Cd²⁺ ions, respectively. Hence, tunable solid‐state fluorescence and selective metal‐ion‐sensor properties were demonstrated in a single organic material.     

Stimulus‐Triggered Formation of an Anion–Cation Exciplex in Copper(I) Complexes as a Mechanism for Mechanochromic Phosphorescence

The investigation of the mechanisms of mechanochromic luminescence is of fundamental importance for the development of materials for photonic sensors, data storage, and luminescence switches. The structural origin of this phenomenon in phosphorescent molecular systems is rarely known and thus the formulation of structure–property relationships remains challenging. Changes in the M–M interactions have been proposed as the main mechanism with d¹⁰ coinage metal compounds. Herein, we describe a new mechanism—a mechanically induced reversible formation of a cation–anion exciplex based on Cu–F interactions—that leads to highly efficient mechanochromic phosphorescence and unusual large emission shifts from UV‐blue to yellow for Cu^I complexes. The low‐energy luminescence is thermo‐ and vaporesponsive, thus allowing the generation of white light as well as for recovering the original UV‐blue emission.     

Poly(N‐vinyl pyrrolidone)‐block‐Poly(N‐vinyl carbazole)‐block‐poly(N‐vinyl pyrrolidone) triblock copolymers: Synthesis via RAFT/MADIX process,self‐assembly behavior,and photophysical properties

Poly(N‐vinyl pyrrolidone)‐block‐poly(N‐vinyl carbazole)‐block‐poly(N‐vinyl pyrrolidone) (PVP‐b‐PVK‐b‐PVP) triblock copolymers were synthesized via sequential reversible addition‐fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) process. First, 1,4‐phenylenebis(methylene)bis(ethyl xanthate) was used as a chain transfer agent to mediate the radical polymerization of N‐vinyl carbazole (NVK). It was found that the polymerization was in a controlled and living manner. Second, one of α,ω‐dixanthate‐terminated PVKs was used as the macromolecular chain transfer agent to mediate the radical polymerization of N‐vinyl pyrrolidone (NVP) to obtain the triblock copolymers with various lengths of PVP blocks. Transmission electron microscopy (TEM) showed that the triblock copolymers in bulks were microphase‐separated and that PVK blocks were self‐organized into cylindrical microdomains, depending on the lengths of PVP blocks. In aqueous solutions, all these triblock copolymers can self‐assemble into the spherical micelles. The critical micelle concentrations of the triblock copolymers were determined without external adding fluorescence probe. By analyzing the change in fluorescence intensity as functions of the concentration, it was judged that the onset of micellization occurred at the concentration while the FL intensity began negatively to deviate from the initial linear increase with the concentration. Fluorescence spectroscopy indicates that the self‐assembled nanoobjects of the PVP‐b‐PVK‐b‐PVP triblock copolymers in water were capable of emitting blue/or purple fluorescence under the irradiation of ultraviolet light. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1852–1863     

1,2,5-Triphenylpyrrole Derivatives with Dual Intense Photoluminescence in Both Solution and the Solid State: Solvatochromism and Polymorphic Luminescence Properties

Five organic luminophores, 1,2,5-triphenylpyrrole (TPP) derivatives 3 a – e bearing electron-withdrawing or electron-donating groups, have been synthesized by Pd-catalyzed Suzuki coupling of 1-phenyl-2,5-di(4′-bromophenyl)pyrrole and para-substituted phenylboronic acid derivatives. They possess good thermal stabilities with high decomposition temperatures above 310 °C. Investigation of the photophysical properties of the luminogens 3 a – e indicated that they exhibited dual intense photoluminescence in both solution and the solid state due to their twisted conformations, and their fluorescence quantum yields (Φ_F) were determined as 68.7–94.9 % in THF solution and 19.1–52.0 % in solid powder form. Compounds 3 a – c bearing electron-accepting groups exhibited remarkable solvatochromism with large Stokes shifts, attributable to their D-π-A structure and intramolecular charge-transfer effect. In particular, 3 a , bearing aldehyde groups, displayed an obvious red-shift of the emission band from 445 to 564 nm with increasing solvent polarity. However, no obvious solvatochromic behavior was observed for compounds 3 d , e bearing electron-donating groups. The luminophore 3 a exhibited polymorphic luminescence properties and crystallization-induced emission enhancement.     

Tailoring Solution Cast Poly(3,4‐dioctyloxythiophene) Transducers for Potentiometric All‐Solid‐State Ion‐Selective Electrodes

A novel concept of tailoring potentiometric responses of all‐solid‐state ion‐selective electrodes was introduced. The effect of composition and resulting properties of the conjugated polymer transducer, placed between the electrode support and ion‐selective membrane, on analytical characteristic of obtained sensors was studied.     

All Solid State Nickel(II)‐Selective Potentiometric Sensor Based on an Upper Rim Substituted Calixarene

A new ionophore, i.e. p‐(2‐thiazolazo)calix[4]arene ( I ) has been explored for its selective behavior towards Ni(II) ions. A poly(vinyl chloride) based membrane containing ( I ) as an electroactive material along with sodiumtetraphenylborate (NaTPB), and nitrophenyloctyl ether in the ratio 10 : 100 : 3 : 150 (I:PVC:NaTPB:NPOE) (w/w) was used to fabricate an all solid state nickel(II)‐selective sensor. The developed sensor exhibited a working concentration range of 1.0×10^?6–1.0×10^?1 M, with a Nernstian slope of 28.9±1.0 mV/decade of activity and a response time of 10–15 s. This sensor shows a detection limit of 9.0×10^?7 M. Its potential response remains unaffected of pH in the range 3.0–7.6, and the cell assembly could be used successfully in partially nonaqueous medium (up to 10 % v/v) without any significant change in the slope value or the working concentration range. The sensor worked satisfactorily for about ten weeks and exhibited excellent selectivity over a number of mono‐, bi‐, and tri‐valent cations including alkali, alkaline earth metal, and transition metal ions. It could be used as an indicator electrode for the end point determination in the potentiometric titration of nickel ions against ethylenediaminetetraacetic acid (EDTA) as well as for the determination of nickel ion concentration in real samples.     

Lanthanide Luminescence Improvement by Using a Functional Poly(Ionic Liquid) as Matrix and Co‐ligand

A poly(ionic liquid) (BA‐PIL) carrying a benzoic acid group in each repeating unit of the polymer architecture, which has the dual function of acting as a matrix and second ligand, has been developed. Through the incorporation of BA‐PIL with the complex [Ln(hfa)₃] (hfa=hexafluoroacetylacetone) as an emitting precursor, significant luminescence improvement was achieved in the obtained hybrid materials. Confinement of the lanthanide(III) complexes within the rigid chains of the polymer, together with replacement of the coordinated water molecules, are believed to be ascribed to the enhanced optical properties.     

Photo‐Induced Solid‐State Crosslinking of Electrospun Poly(vinyl alcohol) Fibers

Summary: Poly(vinyl alcohol) (PVA) was derivatized by polymer analogous reaction with thienyl acryloyl chloride and processed to submicrometer fibers by electrospinning from aqueous solution. Water solubility of otherwise water‐soluble PVA fibers was reduced considerably by UV crosslinking of thienyl acrylate modified PVA fibers in the solid state. Water stability of these crosslinked fibers was proven by water steam test at 95 °C.

UV/Vis spectrum of PVA‐Thio fibers irradiated for different periods at 300 nm.     

Copolymerization of poly(vinyl alcohol)‐graft‐poly(1,4‐dioxan‐2‐one) with designed molecular structure by a solid‐state polymerization method

Poly(vinyl alcohol)‐graft‐poly(1,4‐dioxan‐2‐one) (PVA‐g‐PPDO) with designed molecular structure was synthesized by a solid‐state polymerization. The solid‐state copolymerization was preceded by a graft copolymerization of PDO initiated with PVA as a multifunctional initiator, and Sn (Oct)₂ as a coininitiator/catalyst in a homogeneous molten state. The polymerization temperature was then decreased and the copolymerization was carried out in a solid state. The products prepared by solid‐state polymerization were characterized by ¹H NMR and DSC, and were compared with those synthesized in the homogeneous molten state. The degree of polymerization (D_p), degree of substitution (D_s), yield and the average molecular weight of the graft copolymer with different molecular structure were calculated from the ¹H NMR spectra. The results show that the crystallization process during the solid‐state polymerization may suppress the undesirable inter‐ or intramolecular side reactions, then resulting in a controlled molecular structure of PVA‐g‐PPDO. The results of DSC measurement show that the molecular structures determine the thermal behavior of the PVA‐g‐PPDO. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3083–3091, 2006     

Bright White‐Light Emission from a Single Organic Compound in the Solid State

White‐light‐emitting materials and devices have attracted enormous interest because of their great potential for various lighting applications. We herein describe the light‐emitting properties of a series of new difunctional organic molecules of remarkably simple structure consisting of two terminal 4‐pyridone push–pull subunits separated by a polymethylene chain. They were found to emit almost “pure” white light as a single organic compound in the solid state, as well as when incorporated in a polymer film. To the best of our knowledge, they are the simplest white‐light‐emitting organic molecules reported to date.