Electronic Conjugation Research Articles

Low-Temperature Photolysis of Benzoyl Peroxide

The photolysis of dry benzoyl peroxide (BP) at 77 K in the 480–236 nm range of wavelengths and an ethanol solution is studied via EPR. It is determined that the main photochemical process in irradiating BP at λ = 480–365 nm is the direct photodissociation of the O–O peroxide bonds and C–H bonds of benzene rings to form benzoyloxy radicals and atomic hydrogen, which likely forms via a two-quantum mechanism. The quantum yield of primary intermediates is φ ≈ 2.7 × 10−5. Upon subsequent irradiation of a sample using light with λ = 300–236 nm, benzoyloxy radicals release carbon dioxide and transform into phenyl radicals with a quantum yield of φ ≈ 3 × 10−4. At 120–145 K, phenyl radicals react with double bonds of aromatic rings of PB to form phenyl-substituted cyclohexadienyl radicals vanishing at 273 K. Quantum chemical calculations of the radical structures of photolyzed peroxide are made with the density functional approach (B3LYP/6-311g), and good agreement between the experimental and theoretical parameters is noted. Calculations show that in the structure of benzoyloxy radicals, the spin density is distributed almost equally between the two oxygen atoms of the radical, due to the conjugation of the unpaired electron to the lone p electron pair on the oxygen atom of the C=O group. In the photolysis of BP solutions in ethanol at λ ≥ 365 nm, solvent radicals form via sensitized photolysis through the reaction between primary benzoyloxy radicals and solvent molecules.

Synthesis and electronic properties of carbazole-based core-modified diporphyrins showing near infrared absorption.

Directly linked carbazole-based core-modified diporphyrin D2 and fused diporphyrin F2 were synthesized. These diporphyrins showed significant electronic interactions and conjugation allowing for redshifted near infrared (NIR) absorption and small HOMO-LUMO gaps as confirmed by NIR absorption spectroscopy, cyclic voltammetry (CV) measurements, and DFT calculations.

Switchable Luminescence of New Compounds Based on Imidazoles and Azomethines

The spectral and luminescent properties of compounds A3–SA, A4–o–SA, and A4–o–K have been studied, whose structures include moieties of triphenylimidazole A3, tetraphenylimidazole A4, and hydroxyazomethines salicylideneaniline SA and coumarin-substituted azomethine K. Due to electronic conjugation of moieties, the compound A3–SA exhibits switchable luminescence only in alcohol solutions, whereas independent behavior of the moieties is observed in the case of linking of these luminophores by an oxygen bridge and luminescence switching by changing the excitation wavelength is possible both in solutions and polymeric media.

Altering the optoelectronic properties of boron difluoride formazanate dyes via conjugation with platinum(II)-acetylides.

The combination of π-conjugated organic compounds and Pt(ii)-acetylides is a powerful strategy for the production of functional optoelectronic materials. The presence of the heavy element, Pt, in these compounds enhances electronic delocalization generally resulting in low-energy absorption and emission maxima and often leads to intersystem crossing, resulting in phosphorescence. When boron complexes of N-donor ligands, such as boron dipyrromethenes (BODIPYs), are involved the molecular and polymeric materials produced have properties that are advantageous for their use as oxygen-sensors, in triplet-triplet annihilation, and as the functional components of photovoltaics. Based on these exciting results, we endeavored to thoroughly examine the effect of Pt(ii)-acetylide conjugation on the properties of BF2 formazanate dyes, which offer improved redox properties and red-shifted absorption and emission bands compared to many structurally related BODIPYs. The results showed that phosphine-supported Pt(ii)-acetylide incorporation enhanced electronic conjugation, rendering the electrochemical reduction of the BF2 formazanate dyes more difficult, while also red-shifting their absorption and emission maxima. Unlike similar BODIPYs, the presence of Pt(ii) did not facilitate phosphorescence, but rather quenched fluorescence. This study provides significant insights into structure-property relationships and guiding principles for the design of BF2 formazanate dyes, a rapidly emerging family of readily accessible optoelectronic materials.

Hyperconjugative aromaticity and protodeauration reactivity of polyaurated indoliums

Aromaticity generally describes a cyclic structure composed of sp2-hybridized carbon or hetero atoms with remarkable stability and unique reactivity. The doping of even one sp3-hybridized atom often damages the aromaticity due to the interrupted electron conjugation. Here we demonstrate the occurrence of an extended hyperconjugative aromaticity (EHA) in a metalated indole ring which contains two gem-diaurated tetrahedral carbon atoms. The EHA-involved penta-aurated indolium shows extended electron conjugation because of dual hyperconjugation. Furthermore, the EHA-induced low electron density on the indolyl nitrogen atom enables a facile protodeauration reaction for the labile Au-N bond. In contrast, the degraded tetra-aurated indolium with a single gem-dimetalated carbon atom exhibits poor bond averaging and inertness in the protodeauration reaction. The aromaticity difference in such two polyaurated indoliums is discussed in the geometrical and electronic perspectives. This work highlights the significant effect of metalation on the aromaticity of polymetalated species.

Enhanced electromagnetic wave absorption of polar absorber hybrids self-assembled by MWCNTs and sulfonated polystyrene microsphere

Polar absorber hybrids containing sulfonic groups with a three-dimensional architecture were self-assembled by the incorporation of sulfonated polystyrene microspheres (PS-SO3H) and multi-walled carbon nanotubes (MWCNTs). The influence of polar sulfonic groups of PS microspheres on the microwave absorption of MWCNTs was presented. The structure and morphology of absorber hybrids were characterized by Raman, FTIR, XPS, SEM and TEM. The results of SEM and TEM proved that the continuous conductive network was constituted and the dispersity of MWCNTs was promoted, which is attributed to the framework support of sulfonated PS microspheres among MWCNTs and self-assembly effect induced by π–π stacking and p–π electron conjugation. The polar absorbers hybrids of PS-SO3H@MWCNTs exhibited preeminent absorbing performance. The maximum reflection loss was − 39.22 dB at 12.33 GHz, and the bandwidth correspond to the reflection loss below − 10 dB was 1.82 GHz. In contrast, the maximum reflection loss of nonpolar PS@MWCNTs hybrid was − 25.22 dB at 9.04 GHz and the bandwidth below − 10 dB was 1.60 GHz. The results indicate that the polar groups have crucial impact on the enhanced absorbing performance, which can help to prepare a promising microwave absorbing materials in 2–18 GHz frequency for absorbing applications.

New approach for biological synthesis of reduced graphene oxide

Graphene synthesis has created great interest because of the potential applications in various fields. Many works of graphene synthesis from chemical reduction of graphene oxide involving harmful reactants have been published. A battery of both aerobic and anaerobic gram-negative and gram-positive strains as well as an extremophile microbial consortium from natural environment (Rio Tinto, Spain) were tested in graphene oxide reduction at simplest operating conditions. Results showed biological reduction of GO by all microorganisms, under aerobic conditions without any nutrient and carbon source addition and at room temperature (20–25 °C). UV–vis spectra of RGO showed the adsorption maximum gradually shifted from 230 nm to 270 nm, indicating an increase in the electronic conjugation. Moreover, G band in Raman spectra of RGO shifted from the original value of 1589 ± 1 cm−1 in GO. TGA analyses indicated that only weak weight losses of 2.5% both at 200 °C and above 300 °C, were achieved for Shewanella baltica strain and extremophile microbial consortium related to the presence of oxygen functional groups, indicating the GO reduction. The main novelty of the present work suggests that RGO biosynthesis was mediated by chemical oxidation independently of the bacterial respiration. The method described in the present work is comparable to other biological as well as physicochemical processes and environmentally friendly taking advantage of natural resources for graphene synthesis.

Diffusion of Multiwall Carbon Nanotubes into Industrial Polymers

Carbon nanotubes (CNTs) are made out of carbon atoms connected in hexagonal shapes, with every carbon molecule covalently attached to three other carbon particles. The properties of nanotubes have made scientists and organizations think about utilizing them in many fields. For instance, since carbon nanotubes have the most noteworthy quality to-weight proportion of any known material. Nanocomposites of adjusted multi walled carbon nanotubes (MWCNTs) installed in a polymer matrix yield a one of a kind mix of warm and electrical properties and mechanical quality. The composites combine the vast pseudo capacitance of the directing polymers with the quick charging/releasing two-fold film impedance and incredible machine-driven possessions of the carbon nanotubes. The electrochemically co-stored composites are the most homogeneous and demonstrate an unordinary communication between the polymer and nanotubes, offering ascend to a reinforced electron delocalisation and conjugation along the polymer chains

Impact of Unsymmetrical Alkyl–Fluoroalkyl Side Chains over Coil-to-Rod Transition of Soluble Polyacetylenes: Modulation of Electronic Conjugation of Isolated Chains and Their Self-Assembly

Soluble all-trans polyacetylenes (PAs) are most ideal models to study the spectroscopic properties of conjugated polymers for precise control of their backbone configurations, resulting in semiconducting properties for optoelectronic applications. Herein, we report precise control of the backbone configuration and subsequent self-assembly of soluble PAs flanked with alkyl–fluoroalkyl side chains, using light and temperature stimuli respectively in solution. PAs with symmetric alkyl and unsymmetrical alkyl–fluoroalkyl side chains were successfully polymerized by living cyclopolymerization with the olefin metathesis reaction mediated by third-generation Grubbs catalysts. Coil-to-rod-like conformational transition was observed for all of the PAs under ambient light due to photoisomerization, monitored by UV–vis spectroscopy and discussed in terms of the Huang–Rhys parameter. Enrichment of the trans configuration in the conjugated backbones opened up the possibility of aggregation between the isolated conjuga...

Electronic Excitations of Polythiophene within Many-Body Perturbation Theory with and without the Tamm-Dancoff Approximation.

Excited electronic states of small and large π-conjugated organic molecules can be described within ab initio many-body perturbation theory, notably by the GW approximation for the electron self-energy operator combined with the Bethe-Salpeter equation for correlated electron-hole excitations. In this context, the Tamm-Dancoff approximation is routinely employed to reduce the computational effort. It is known that the use of this approximation introduces errors of several 100 meV for small organic molecules but is negligible for extended systems. In this paper, we investigate how exactly the transition between these two regimes happens, by calculating the optical excitation energies of a series of polythiophene molecules of different sizes. We determine which parts of the electron-hole interaction are responsible for the deviation and show that the quantitative effects of the Tamm-Dancoff approximation depend sensitively on the size of the electronic system, in particular on the electronic conjugation length.

Preparation and Physical Characterization of Pyrene and Pyrrolo[3,4‐c]pyrrole‐1,4‐dione‐Based Copolymers

Two narrow band‐gap copolymers consisting of 2,7‐bis(5‐(trimethylstannyl)thiophen‐2‐yl)‐4,5,9,10‐tetrakis(2‐ethylhexyloxy)‐pyrene (M1) as an electron‐rich unit and diketopyrrolopyrrole (DPP) as an electron‐deficient unit have been synthesized and characterized for polymer solar cells. The two polymers were prepared by Stille coupling reactions. Two solubilizing alkyl chains (ethylhexyl and octlydodecyl) were attached to the DPP unit in order to evaluate their impact upon the optical and electrochemical characteristics of the two polymers. Poly[4,5,9,10‐tetrakis[(2‐ethylhexyl)oxy]pyrene‐alt‐3,6‐bis(thiophen‐2‐yl)‐2,5‐ bis(2‐octyldodecyl)pyrrole[3,4‐c]pyrrole‐ 1,4(2H,5H)‐dione] (PPEHDT‐DPPODo) and poly[4,5,9,10‐tetrakis((2‐ethylhexyl)oxy)pyren‐alt‐3,6‐bis(thiophen‐2‐yl)‐2,5‐bis(2‐ethylhexyl)pyrrole[3,4‐c]pyrrole‐1,4(2H,5H)‐dione] (PPEHDT‐DPPEH) exhibited high thermal stability with decomposition temperatures over 300 °C. Optical properties showed that PPEHDT‐DPPODo and PPEHDT‐DPPEH have optical band gaps of around 1.40 eV. It is believed that both polymers adopt high planar structures in the thin film, leading to more electronic conjugation along the backbone of the conjugated polymers. Powder X‐ray diffraction revealed that PPEHDT‐DPPODo and PPEHDT‐DPPEH seem to have an amorphous nature. The HOMO energy levels of the two polymers are clearly affected by changing alkyl chains. The HOMO levels of PPEHDT‐DPPODo and PPEHDT‐DPPEH were found to be at −5.27 and −5.38 eV, respectively. PPEHDT‐DPPODo showed a HOMO energy level approximately 0.11 eV shallower than that of PPEHDT‐DPPEH, which is probably a consequence of attaching a larger alkyl chain to the DPP moiety reducing its electron accepting ability.

Reaction Kinetics of Reducing Graphene Oxide at Individual Sheet Level Studied by Twilight Fluorescence Microscopy

Kinetics of the reduction reaction of graphene oxide (GO) by l-ascorbic acid in a solution was examined by direct observation of an individual GO sheet with an area over 100 μm2 using Twilight fluorescence microscopy. Temporal changes of either increase in absorbance or decrease in autofluorescence from an individual GO sheet of a known layer number and an area were analyzed by the pseudo-first-order model, the pseudo-second-order model, and the Elovich model. An increase in the absorbance around 600 nm probes an extension of the π–electron conjugation length over multiple hexagonal units. All data at various conditions are best fitted with the Elovich model, implying that the activation energy increases as the reaction progresses. A decrease in the total autofluorescence intensity follows local deoxygenation of oxides. In this case, the pseudo-second-order model, which is based on a homogeneous surface with a constant activation energy, shows the best fit to all data. These results demonstrate that, for ...

Forging Ru–Csp2 Bonds in Paddlewheel Complexes Using the Lithium–Halogen Exchange Reaction

Reported herein are the first examples of the formation of Ru-Csp2 bonds in paddlewheel diruthenium species. A series of six Ru2( ap)4(C6H4-4-X) type compounds ( ap = 2-anilinopyridinate; X = NMe2 (1), N,N-(C6H4-4-OMe)2 (2), tBu (3), H (4), Br (5), CF3 (6)) was synthesized by employing the lithium-halogen exchange reaction with a variety of para-substituted aryl halides. These compounds have been characterized via electronic absorption spectroscopy, cyclic voltammetry, mass spectrometry, and magnetism studies, and their molecular structures have been established by single-crystal X-ray diffraction studies. All compounds are in the Ru25+ oxidation state, with a ground-state electronic configuration of σ2π4δ2(π*δ*)3. Crystal structures of 1-6 confirm this, indicating a Ru-Ru bond order of 2.5. Electrochemical data suggest that the σ-aryls are stronger donors than the σ-alkynyls. A range of electronically different substituents allows for a closer inspection of the extent of electronic conjugation across the diruthenium paddlewheel core and the axial aryl ligand.

Rod-like transition first or chain aggregation first? ordered aggregation of rod-like poly(p-phenyleneethynylene) chains in solution.

The rod-like configuration of conjugated polymer chains with its low energetic disorder is the key to utilizing the backbone as a highly electrically-conductive wire. An energetic disorder that is higher than 0.1 eV, coupled with vibronic modes of the chains, leads to the localization of charges. Herein, we have tracked precisely the rod-like transition of poly(p-phenyleneethynylene) (PPE) chains as a function of temperature in diluted solutions, and shown a steep increase in persistence length at 230 K. The resulting rod-like configuration of the PPE chains with its extended electronic conjugation exhibited an extremely small energetic disorder of ∼70 meV, and was stabilized by subsequent polymer aggregate formation.

Substituted polyfluoroaryl interactions with an arginine side chain in galectin-3 are governed by steric-, desolvation and electronic conjugation effects.

In the β-d-galactopyranoside-binding protein galectin-3, synthetic inhibitors substituted at the 3-position of a thiodigalactoside core cause the formation of an aglycone binding pocket through the displacement of an arginine residue (Arg144) from its position in the apoprotein. To examine in detail the role of different molecular interactions in this pocket, we have synthesized a series of nine 3-(4-(2,3,5,6-tetrafluorophenyl)-1,2,3-triazol-1-yl)-thiogalactosides with different para substituents and measured their affinities to galectin-3 using a fluorescence polarization assay. High-resolution crystal structures (<1.3 Å) have been determined for five of the ligands in complex with the C-terminal domain of galectin-3. The binding affinities are rationalised with the help of the three-dimensional structures and quantum-mechanical calculations. Three effects seem to be involved: Firstly, the binding pocket is too small for the largest ligands with ethyl and methyl. Secondly, for the other ligands, the affinity seems to be determined mainly by desolvation effects, disfavouring the polar substituents, but this is partly counteracted by the cation-π interaction with Arg144, which stacks on top of the substituted tetrafluorophenyl group in all complexes. The results provide detailed insight into interactions of fluorinated phenyl moieties with arginine-containing protein binding sites and the complex interplay of different energetic components in defining the binding affinity.

Substitution Effect on the Charge Transfer Processes in Organo-Imido Lindqvist-Polyoxomolybdate.

Two new aromatic organo-imido polyoxometalates with an electron donor triazole group ([n-Bu4N]2[Mo6O18NC6H4N3C2H2]) (1) and a highly conjugated fluorene ([n-Bu4N]2[Mo6O18NC13H9]) (2) have been obtained. The electrochemical and spectroscopic properties of several organo-imido systems were studied. These properties were analysed by the theoretical study of the redox potentials and by means of the excitation analysis, in order to understand the effect on the substitution of the organo-imido fragment and the effect of the interaction to a metal centre. Our results show a bathochromic shift related to the charge transfer processes induced by the increase of the conjugated character of the organic fragment. The cathodic shift obtained from the electrochemical studies reflects that the electronic communication and conjugation between the organic and inorganic fragments is the main reason of this phenomenon.

Third order nonlinear optical properties of DNA-based biopolymers thin films doped with selected natural chromophores

The results of linear and nonlinear optical (NLO) studies on thin films of DNA based biopolymers, doped with natural chromophores extracts of sweet paprika, turmeric as well as curry leaves are reported and discussed. The thin films were obtained by spin coating on glass substrates. The spectroscopy measurements show that the extracts absorb in visible, at different wavelengths, revealing an important π electron conjugation. The nonlinear optical measurements, done by the optical third harmonic generation technique at 1064.2 nm fundamental wavelength, show that the fast, electronic origin third order NLO susceptibility of natural extracts χ(3)(−3ω;ω,ω,ω), is large and comparable or higher than that measured for synthetic counterparts. The largest one in this study was found for the curry leaves extract: (396.9 ± 40) ×10−14 esu.

Carbon-nanotube/sulfur cathode with in-situ assembled Si3N4/graphene interlayer for high-rate and long cycling-life lithium-sulfur batteries

A Si3N4/graphene composite is designed as an interlayer for a carbon-nanotubes/sulfur cathode to improve electrochemical performance of lithium-sulfur batteries. In the interlayer, Si3N4 nanoparticles suppress the migration of the dissolved polysulfides and graphene sheets construct a 3-dimensional charge-transfer network. The carbon-nanotubes/sulfur@Si3N4/graphene cathode delivers an initial discharge capacity of 1334.7 mAh g−1 at 0.1 C and retains a capacity as high as 745.8 mAh g−1 after 200 cycles, with a capacity fade ratio of 0.22% per cycle. The cathode shows good cycling life, delivering a discharge capacity of 413.3 mAh g−1 for 1 C after 1000 cycles. According to the results of density functional theory calculation, the anchoring of the Si3N4/graphene interlayer to lithium polysulfide can be attributed to a coefficient chemical binding of Li-N and Si-S bonds generating from electronic conjugation effect between the Si3N4 supercell surface and the polysulfides. Generally, the improvement in electrochemical performance originates from the enhancements in Li+ diffusion coefficient and charge transfer, and from the restraining of the shuttle effect of the dissolved lithium polysulfide as a result of the Si3N4/graphene interlayer.

Electronically Coupled, Two-Dimensional Assembly of Cu1.1S Nanodiscs for Selective Vapor Sensing Applications

We study temperature-dependent charge transport in two-dimensional assemblies of copper sulfide nanodiscs in the covellite crystal phase (Cu1.1S). To enhance interparticle coupling, we cross-link the nanocrystals with the organic π-system Cu-4,4′,4″,4‴-tetraaminophthalocyanine and observe an increase in the conductivity by 6 orders of magnitude. The electrical properties of monolayers of this hybrid ensemble are consistent with a two-dimensional semiconductor and exhibit two abrupt changes at discrete temperatures (120 and 210 K), which may be interpreted as phase changes. X-ray scattering experiments serve to study the importance of electronic conjugation in the organic π-system vs interparticle spacing for efficient charge transport. Applying the hybrid ensemble as a chemiresistor in organic vapor sensing experiments reveals a strong selectivity between polar and nonpolar analytes, which we discuss in light of the role of the organic π-system and its metal center.

Theoretical Study on Structure and Electronic Properties of Aniline-5-Membered Heterocyclic Co-oligomers

With the aim of exploring the electronic and optical properties of some interesting conductive copolymers in view of potential applications, a regular oligomer systems made of aniline and three reference heterocyclic compounds (pyrrole, thiophene and furan) are studied using density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations at B3LYP/6-31+G(d,p) level. It was found that poly (aniline-co-pyrrole) has the lowest ionization potential (4.48 eV) and electro affinity (0.77 eV) while poly (aniline-co-thiophene) has lowest band gap and longest (3.21 eV) wavelength of absorption (and then highest electronic conjugation) among the studied molecules. Comparison of the theoretical data and spectroscopic results obtained by DFT calculations with those experimentally obtained show very good agreement.