Conjugated Copolymers That Shouldn't Be

Triangular Triazine-Triphenylamine Functionalized Hybrid Fluorescent Porous Polymers for Detection and Photodegradation of Tetracycline Hydrochloride

First, an organic semiconductor fluorescent molecule of 4',4″,4"'-(2,4,6-triphenyl-1,3,5-triazine)-4-(N,N-diphenyl-(1,1'-biphenyl)-4-amine (TPTz) is successfully synthesized by the Suzuki-Miyaura coupling reaction of 2,4,6-tris(4-bromophenyl)-1,3,5-triazine with 4-(diphenylamino)phenylboronic acid. TPTz offers as high as 85% fluorescence quantum yield and a strong solvent effect, with fluorescent colors across the visible spectrum in different solvents. Then, an organic-inorganic hybrid fluorescent porous polymer of PCS-TPTz with a surface area of 714 m2 g-1 and pore volume of 0.660 cm3 g-1 is prepared by the Friedel-Crafts reaction of TPTz and octavinylsilsesquioxane; PCS-TPTz showed a high fluorescence quantum yield of 17% with a large Stokes shift of up to 280 nm. The excellent fluorescence properties and insolubility of PCS-TPTz make it to act as a heterophase sensor for tetracycline hydrochloride (TH) with a KSV of 2.39 × 104 M-1. In addition, PCS-TPTz exhibits an excellent photodegradation activity for antibiotic TH without the requirement for additional oxidants or pH adjustments. ESR spectra and free radical trapping experiment indicate that superoxide radical (•O2-) is the active radical for achieving the photodegradation. The simultaneous detection and degradation of TH are achieved by PCS-TPTz.

Conjugation through Si-O-Si bonds, silsesquioxane (SQ) half cage copolymers, extended examples via SiO0.5/SiO1.5 units: multiple emissive states in violation of Kasha's rule

We previously reported that phenyl- and vinyl-silsesquioxanes (SQs), [RSiO1.5]8,10,12 (R = Ph or vinyl) functionalized with three or more conjugated moieties show red-shifted absorption- and emission features suggesting 3-D conjugation via a cage centered LUMOs. Corner missing [PhSiO1.5]7(OSiMe3)3 and edge opened, end capped [PhSiO1.5]8(OSiMe2)2 (double decker, DD) analogs also offer red shifted spectra again indicating 3-D conjugation and a cage centered LUMO. Copolymerization of DD [PhSiO1.5]8(OSiMevinyl)2 with multiple R-Ar-Br gives copolymers with emission red-shifts that change with degree of polymerization (DP), exhibit charge transfer to F4TNCQ and terpolymer averaged red-shifts suggesting through chain conjugation even with two (O-Si-O) end caps possibly via a cage centered LUMO. Surprisingly, ladder (LL) SQ, (vinylMeSiO2)[PhSiO1.5]4(O2SiMevinyl) copolymers offer emission red-shifts even greater for analogous copolymers requiring a different explanation. Here we assess the photophysical behavior of copolymers of a more extreme SQ form: the half cage [PhSiO1.5]4(OSiMe2Vinyl)4, Vy4HC SQs. We again see small red-shifted absorptions coupled with significant red-shifted emissions, even with just a half cage, thus further supporting the existence of pπ-dπ and/or σ*-π* conjugation through Si-O-Si bonds and contrary to most traditional views of Si-O-Si linked polymers. These same copolymers donate an electron to F4TCNQ generating the radical anion, F4TCNQ-. as further proof of conjugation. Column chromatographic separation of short from longer chain oligomers reveals a direct correlation between DP and emission λmax red-shifts as another indication of conjugation. Further, one- and two-photon absorption and emission spectroscopy reveals multiple excited fluorescence-emitting states in a violation of Kasha's rule wherein emission occurs only from the lowest excited state. Traditional modeling studies again find HOMO LUMO energy levels residing only on the aromatic co-monomers rather than through Si-O-Si bonds as recently found in related polymers.

New Janus Tricyclic Laddersiloxanes: Synthesis, Characterization, and Reactivity

The synthesis of four novel syn-type tricyclic laddersiloxanes bearing eight or six alkenyl groups is presented. These compounds possess reactive alkenyl groups on both the bridged and side silicon atoms, and their structures were determined through characterization using multinuclear 1D and 2D NMR spectroscopy, mass spectrometry, and elemental analysis techniques. To investigate their reactivity, the compounds were subjected to hydrosilylation using two different silanes, and the resulting fully hydrosilylated compounds were thoroughly analyzed. Remarkably, all the synthesized laddersiloxanes displayed high thermal stability, suggesting their potential as promising precursors for the development of new hybrid materials. Additionally, preliminary findings indicate the possibility of exploiting the reactivity difference between the alkenyl groups attached to the D- and T-unit silicon atoms for the synthesis of Janus molecules. These findings highlight the potential of the reported compounds as valuable building blocks in the construction of innovative materials.

Synthesis of unsymmetrically and symmetrically functionalized disiloxanes via subsequent hydrosilylation of C≡C bonds

A selective synthesis of unsymmetrically functionalized disiloxanes via the subsequent hydrosilylation of internal alkynes in the first step, and alkynes (terminal or internal) or 1,3-diynes in the second, with 1,1,3,3-tetramethyldisiloxane (1) is presented for the first time. Using developed approaches performed in a stepwise or one-pot manner a new family of disubstituted disiloxanes was obtained which had previously been inaccessible by other synthetic methods. Moreover, symmetrically functionalized disiloxanes were obtained by direct hydrosilylation of 2 equivalents of terminal or internal alkynes with 1, showing the unique versatility of the hydrosilylation process. Three examples of symmetric disiloxanes were characterized by single crystal X-ray diffraction for the first time. As a result, a wide group of new compounds which can find potential applications as building blocks or coupling agents was obtained and characterized.

Novel hybrid composites based on double-decker silsesquioxanes functionalized by methacrylate derivatives and polyvinyl alcohol as potential materials utilized in biomedical applications

The use of diverse biomaterials for regenerative medicine is constantly evolving. Therefore, looking for easy-to-scale-up materials in terms of preparation, less complex composition, and featuring structural and chemical stability seems justified. In this work, we report the preparation of double-decker silsesquioxane-based (DDSQ-based) composites, which, according to our best knowledge, have never been used as biomaterials. A family of methacrylate-substituted DDSQs was obtained starting from the previously reported hydroxyalkyl double-decker silsesquioxanes. In the resulting hybrids, methacrylate groups are attached to each other's lateral silicon atoms of DDSQ in trans positions, providing an excellent geometry for forming thin layers. In contrast to pure organic methacrylates, the covalent bonding of methacrylate derivatives to inorganic silsesquioxane core improves mechanics, cell adhesion, and migration properties. Furthermore, to increase the hydrophilicity of the resulting DDSQ-based hybrids, polyvinyl alcohol (PVA) was added. The entire system forms an easy-to-obtain two-component (DDSQ-PVA) composite, which was subjected without any upgrading additives to biological tests later in the research. The resulting biomaterials fulfill the requirements for potential medical applications. Human fibroblasts growing on prepared hybrid composites are characterized by proper spindle-shaped morphology, proliferation, and activation status similar to control conditions (cells cultured on PVA), as well as increased adhesion and migration abilities. The obtained results suggest that the prepared biomaterials may be used in regenerative medicine in the future.

Charge transport of F4TCNQ with different electronic states in single-molecule junctions

The molecular conductance of 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyano-quinodimethane (F4TCNQ) with different electronic states (neutral, radical anion, and dianion) was investigated by the scanning tunneling microscope break junction (STM-BJ) technique. These electronic states have distinct conductance, and the conductance decreases in the order of neutral > radical anion > dianion. Surprisingly, the molecular conductance of the neutral F4TCNQ junction reaches 10^-1.17G₀, attributed to its LUMO energy level being close to the Fermi level of the gold electrode. Moreover, we found that neutral F4TCNQ can be gradually reduced to radical anions under a relatively low bias voltage of 100 mV. These results will advance the development of organic optoelectronic devices and molecule electronics.

Distinct insight into the use of difunctional double-decker silsesquioxanes as building blocks for alternating A–B type macromolecular frameworks

A distinct look at known, hydrosilylation reactions used for the formation of DDSQ-based linear A–B alternating macromolecular systems with DPn > 1000 is presented. Selected physicochemical properties of obtained hybrid co-polymers were determined.

Plastic and Waste Tire Pyrolysis Focused on Hydrogen Production—A Review

In this review, we compare hydrogen production from waste by pyrolysis and bioprocesses. In contrast, the pyrolysis feed was limited to plastic and tire waste unlikely to be utilized by biological decomposition methods. Recent risks of pyrolysis, such as pollutant emissions during the heat decomposition of polymers, and high energy demands were described and compared to thresholds of bioprocesses such as dark fermentation. Many pyrolysis reactors have been adapted for plastic pyrolysis after successful investigation experiences involving waste tires. Pyrolysis can transform these wastes into other petroleum products for reuse or for energy carriers, such as hydrogen. Plastic and tire pyrolysis is part of an alternative synthesis method for smart polymers, including semi-conductive polymers. Pyrolysis is less expensive than gasification and requires a lower energy demand, with lower emissions of hazardous pollutants. Short-time utilization of these wastes, without the emission of metals into the environment, can be solved using pyrolysis. Plastic wastes after pyrolysis produce up to 20 times more hydrogen than dark fermentation from 1 kg of waste. The research summarizes recent achievements in plastic and tire waste pyrolysis development.

Polymethacrylates containing cage-silsesquioxanes in the side chains: effects of cage and linker structures on film properties

Polymers in which cage-silsesquioxanes were tethered through urethane linkers, were newly synthesized. The free-standing films were supported by the hydrogen bonding networks. Their properties were dependent on the cage structure.

Unconventional Conjugation in macromonomers and polymers

Multiple reviews have been written concerning conjugated macromonomers and polymers both as general descriptions and for specific applications. In most examples, conjugation occurs via elec-tronic communication via continuous overlap of...

Hydroxyalkyl-substituted double-decker silsesquioxanes: effective separation of cis and trans isomers

A procedure to sequentially crystallize the two isomers of hydroxyalkyl-substituted double-decker silsesquioxanes from one another, which may result in the preparation of new materials and polymers with well-defined properties, is reported.

Unexpected and frustrating transformations of double-decker silsesquioxanes

This paper outlines an unexpected type of intramolecular transformation of DDSQ during hydrolytic condensation and surprising catalytic reactivity in silylative coupling.

Vinyl- and chloromethyl-substituted mono-T8 and double-decker silsesquioxanes as specific cores to low generation dendritic systems

We report the series of G1 and G1.5 dendritic systems with mono-T₈ SQs and DDSQ as specific types of dendron and dendrimer cores, respectively. The trivinyl- and tri(chloromethyl)-derivatives were obtained via hydrolytic condensation followed by the hydrosilylation reaction, optimized to yield selectively β-products. Their structures were confirmed by spectroscopic and XRD analyses. It is the first example of double-decker SQs used as cores for the construction of a low generation of dendrimer featuring specific dumbbell frameworks expanding in two or four directions.

Beads on a Chain Fluorescent Oligomeric Materials: Interactions of Conjugated Organic Cross-Linkers with Silsesquioxane Cages

Organic electronic materials have advantages over inorganics in terms of versatility, cost, and processability. Recent advancements in organic materials for light-emitting diodes (OLED), field effect transistors (OFET), and photovoltaics have engendered extensive innovation potential on this field. In this research, we focus on synthesizing SQ (silsesquioxane) based oligomers cross-linked by dibromo-aromatic linkers and explore how the cross-linker influences their photophysical properties. Bis-trialkoxy silyl (linker) model compounds were synthesized to compare noncage photophysical properties with the oligomers. Several techniques such as UV/vis, fluorescence, FTIR, and thermal gravimetric analysis (TGA) have been used to characterize the systems. Time-resolved fluorescence and femtosecond transient absorption spectroscopy were used to understand the excited state dynamics of these materials. Studies were carried out to understand the differences between monomers and oligomers and potential energy transfer and charge transfer between the cages and cross-linking chromophores. Transient absorption showed lower energy absorption from the excited states, suggesting short-range communication between moieties. Single photon counting studies have shown distinct lifetime differences between most linkers and cages display possible excitation energy transfer through these materials. Transient absorption anisotropy measurements have shown signatures for excitation energy transfer between linker chromophores for oligomeric compounds. The silsesquioxane (SQ) backbone of the oligomers gives substantial thermal stability as well as solution processability, giving better flexibility for achieving energy transfer between linking chromophores.

Double-Decker Silsesquioxanes Self-Assembled in One-Dimensional Coordination Polymeric Nanofibers with Emission Properties

The urgent needs for photoactive materials in industry drive fast evolution of synthetic procedures in many branches of chemistry, including the chemistry of silsesquioxanes. Here, we disclose an effective protocol for the synthesis of novel double-decker silsesquioxanes decorated with two (styrylethynylphenyl)terpyridine moieties (DDSQ_Ta-b). The synthesis strategy involves a series of silylative and Sonogashira coupling reactions and is reported for the first time. DDSQ_Ta-b were employed as nanocage ligands to promote self-assembly in the presence of transition metals (TM), i.e., Zn2+, Fe2+, and Eu3+ ions, to form one-dimensional (1D) coordination polymeric nanofibers. Additionally, ultraviolet-promoted and reversible E-Z isomerization of the C═C bond within the ligand structures may be exploited to tune their emission properties. These findings render such complexes promising candidates for applications in materials chemistry. This is the first example of 1D coordination polymers bearing DDSQ-based nodes with TM ions.