Synthesis of 3,4-Bis(benzylidene)cyclobutenes

The syntheses of several derivatives of 3,4-bis(benzylidene)cyclobutene are reported. Previously unknown 1,2-dibromo-3,4-bis(benzylidene)cyclobutene was obtained through in situ generation of 1,6-diphenyl-3,4-dibromo-1,2,4,5-tetraene followed by electrocyclic ring closure. Ensuing reduction and metal-catalyzed cross-coupling provided additional derivatives. The effects of ring strain on the geometry and electronics of these derivatives were examined by X-ray crystallography and ¹H NMR spectroscopy, respectively.National Science Foundation (U.S.)United States. Army Research OfficeMassachusetts Institute of Technology. Institute for Soldier Nanotechnologie

The Synthesis of Azaperylene-9,10-dicarboximides

The syntheses of two azaperylene 9,10-dicarboximides are presented. 1-Aza- and 1,6-diazaperylene 9,10-dicarboximides containing a 2,6-diisopropylphenyl substituent at the N-imide position were synthesized in two steps starting from naphthalene and isoquinoline derivatives

Photoluminescent Energy Transfer from Poly(phenyleneethynylene)s to Near-Infrared Emitting Fluorophores

Photoluminescent energy transfer was investigated in conjugated polymer-fluorophore blended thin films. A pentiptycene-containing poly(phenyleneethynylene) was used as the energy donor, and 13 fluorophores were used as energy acceptors. The efficiency of energy transfer was measured by monitoring both the quenching of the polymer emission and the enhancement of the fluorophore emission. Near-infrared emitting squaraines and terrylenes were identified as excellent energy acceptors. These results, where a new fluorescent signal occurs in the near-infrared region on a completely dark background, offer substantial possibilities for designing highly sensitive turn-on sensors.National Institute of General Medical Sciences (U.S.) (F32GM086044)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (DAAD-19-02-0002

Wireless gas detection with a smartphone via rf communication

Chemical sensing is of critical importance to human health, safety, and security, yet it is not broadly implemented because existing sensors often require trained personnel, expensive and bulky equipment, and have large power requirements. This study reports the development of a smartphone-based sensing strategy that employs chemiresponsive nanomaterials integrated into the circuitry of commercial near-field communication tags to achieve non-line-of-sight, portable, and inexpensive detection and discrimination of gas-phase chemicals (e.g., ammonia, hydrogen peroxide, cyclohexanone, and water) at part-per-thousand and part-per-million concentrations.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001)Deshpande Center for Technological InnovationNational Institutes of Health (U.S.) (National Cancer Institute (U.S.) Ruth L. Kirschstein National Research Service Award F32CA157197

Rapid prototyping of carbon-based chemiresistive gas sensors on paper

Chemically functionalized carbon nanotubes (CNTs) are promising materials for sensing of gases and volatile organic compounds. However, the poor solubility of carbon nanotubes hinders their chemical functionalization and the subsequent integration of these materials into devices. This manuscript describes a solvent-free procedure for rapid prototyping of selective chemiresistors from CNTs and graphite on the surface of paper. This procedure enables fabrication of functional gas sensors from commercially available starting materials in less than 15 min. The first step of this procedure involves the generation of solid composites of CNTs or graphite with small molecule selectors—designed to interact with specific classes of gaseous analytes—by solvent-free mechanical mixing in a ball mill and subsequent compression. The second step involves deposition of chemiresistive sensors by mechanical abrasion of these solid composites onto the surface of paper. Parallel fabrication of multiple chemiresistors from diverse composites rapidly generates cross-reactive arrays capable of sensing and differentiating gases and volatile organic compounds at part-per-million and part-per-thousand concentrations.Massachusetts Institute of Technology. Institute for Soldier NanotechnologiesNational Cancer Institute (U.S.) (Ruth L. Kirschstein National Research Service Award F32CA157197

Spray-Layer-by-Layer Carbon Nanotube/Electrospun Fiber Electrodes for Flexible Chemiresistive Sensor Applications

Development of a versatile method for incorporating conductive materials into textiles could enable advances in wearable electronics and smart textiles. One area of critical importance is the detection of chemicals in the environment for security and industrial process monitoring. Here, the fabrication of a flexible, sensor material based on functionalized multi-walled carbon nanotube (MWNT) films on a porous electrospun fiber mat for real-time detection of a nerve agent simulant is reported. The material is constructed by layer-by-layer (LbL) assembly of MWNTs with opposite charges, creating multilayer films of MWNTs without binder. The vacuum-assisted spray-LbL process enables conformal coatings of nanostructured MWNT films on individual electrospun fibers throughout the bulk of the mat with controlled loading and electrical conductivity. A thiourea-based receptor is covalently attached to the primary amine groups on the MWNT films to enhance the sensing response to dimethyl methylphosphonate (DMMP), a simulant for sarin nerve agent. Chemiresistive sensors based on the engineered textiles display reversible responses and detection limits for DMMP as low as 10 ppb in the aqueous phase and 5 ppm in the vapor phase. This fabrication technique provides a versatile and easily scalable strategy for incorporating conformal MWNT films into three-dimensional substrates for numerous applications.United States. Army Research Office. Institute for Soldier Nanotechnologies (Contract No. DAAD-19–02–0002

Precursor Routes to Conducting Polymers from the Ring-Opening Metathesis Polymerization of Cyclic Olefins

Chapter 1 provides an introduction to the field of conductive polymers. The perspective is that of a chemist who is also interested in the physics of conductive polymers. The concepts discussed in this chapter are referred to throughout the other chapters, and should be a good primer for newcomers to this field as well as a reference to the literature for others. This chapter sets the stage for the theme of this thesis, which is the use of soluble precursor polymers in the synthesis of conductive polymers. Recent work was cited in this chapter which is not available in existing reviews of conductive polymers. The method of ring-opening metathesis polymerization (ROMP) is discussed in Chapter 2. The concepts discussed therein are again referred to throughout the following chapters. The ideas of catalyst matching for different monomers are discussed, and particular emphasis is given to the steric requirements of the catalysts. The ROMP of derivatives of dimethylene cyclobutene is discussed in Chapter 3. However, the primary focus of the chapter is on the polymer polydiisopropylidenecyclobutene. This material is distinctly different from other conductive polymers in the fact that it has a structure consisting of triene units that are mutually orthogonal to each other. A detailed study of this material with a variety of spectroscopies and measurements is presented. The synthesis of polybenzvalene, and the isomerization of this material to polyacetylene, is discussed in Chapter 4. This work constitutes a new precursor method to this fundamentally important polymer, as well as a demonstration of the far reaching scope of ROMP. Polybenzvalene is also a high energy material and has unusual explosive properties which are also discussed. In Chapter 5, new precursor routes to conductive polymers based on the elimination and hydrolysis of ketals are presented. This work has been primarily focused on structural chemistry and how to best transform the precursor polymers into conductive polymers. The majority of the effort has been focused on the, poly (quinone bisketals); however, another example of this concept is presented briefly.</p

Poly(3-hexylthiophene)-block-poly(pyridinium phenylene)s: Block Polymers of p- and n-Type Semiconductors

Conjugated crystalline−crystalline donor−acceptor−donor block copolymer semiconductors, with regioregular poly(3-hexylthiophene) as a donor (p-type) block and poly(pyridinium pheneylene) as an acceptor (n-type) block within the backbone, were produced by sequential Grignard metathesis synthesis of poly(3-hexylthiophene), a Yamamoto-type cross-coupling polymerization−cyclization sequence. These conjugated block copolymers are soluble in organic solvents and display broad optical absorption bands extending close to the near-infrared region. They show reversible ambipolar redox properties with high electron affinities of 3.8−4.0 eV as well as useful ionization potentials of 5.1 eV that are characteristic of the respective blocks. Block copolymers from p- and n-type organic semiconductors are of interest for the formation of nanostructured bulk heterojunctions in photovoltaic devices.National Science Foundation (DMR-1005810)Toray Industries Inc

Bispyridinium-phenylene-based copolymers: low band gap n-type alternating copolymers

Bispyridinium-phenylene-based conjugated donor–acceptor copolymers were synthesized by a Stille cross-coupling and cyclization sequence. These polyelectrolytes are freely soluble in organic solvents and display broad optical absorption bands that extend into the near-infrared region. They show ambipolar redox properties with high electron affinities (LUMO levels) of 3.9–4.0 eV as well as high degrees of electroactivity. When reduced (n-doped) these materials display in situ conductivities as high as 180 S/cm. The high conductivity is attributed to the planar structure that is enforced by the cyclic structures of the polymer. The electron affinities are compared to PCBM, a C[subscript 60] based n-type material and hence may find utility in photovoltaic devices.National Science Foundation (U.S.) (DMR-0706408

Conjugated Amplifying Polymers for Optical Sensing Applications

Thanks to their unique optical and electrochemical properties, conjugated polymers have attracted considerable attention over the last two decades and resulted in numerous technological innovations. In particular, their implementation in sensing schemes and devices was widely investigated and produced a multitude of sensory systems and transduction mechanisms. Conjugated polymers possess numerous attractive features that make them particularly suitable for a broad variety of sensing tasks. They display sensory signal amplification (compared to their small-molecule counterparts) and their structures can easily be tailored to adjust solubility, absorption/emission wavelengths, energy offsets for excited state electron transfer, and/or for use in solution or in the solid state. This versatility has made conjugated polymers a fluorescence sensory platform of choice in the recent years. In this review, we highlight a variety of conjugated polymer-based sensory mechanisms together with selected examples from the recent literature.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologie