Tuning of the electronic properties of H‐passivated armchair graphene nanoribbons by mild border oxidation: Theoretical study on periodic models

We report the results of a DFT study of the electronic properties, intended as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, of periodic models of H‐passivated armchair graphene nanoribbons (a‐GNRs) as that synthetized by bottom‐up technique, functionalized by vicinal dialdehydic groups. This material can be obtained by border oxidation in mild and easy to control conditions with ¹Δ_g O₂ as we reported in our previous paper (Ghigo et al., ChemPhysChem 2015, 16, 3030). The calculations show that the two models of border oxidized a‐GNRs (model A, 0.98 nm and model B, 1.35 nm wide) present LUMO and HOMO energies lowered by an extend roughly linearly dependent on the amount of oxygen chemically bound. The frontier orbital energy variations dependence on the % wt of oxygen bound are, for model A: ?0.12 eV for the LUMO and ?0.05 eV for the HOMO; for model B: ?0.15 eV (HOMO) and ?0.06 eV (LUMO). © 2016 Wiley Periodicals, Inc.     

The Synthesis and Some Chemical Properties of New 1,2:5,6-DI-O-Isopropylidene-α -D-Glucofuranose Hydrophosphoryl Derivatives

Methods for the synthesis of major monosaccharide hydrophosphoryl derivatives have been developed with the phosphorylation of 1,2:5,6-di-O-isopropylidene-α -D-glucofuranose (diacetoneglucose) as an example. The study of their chemical transformations has been launched.     

Chemical studies of carbohydrates (II) On the mechanism of the conversion of a glucose derivative into a pyridazine compound

The formation of 3-(2′,2′-dimethyl-1′,3′-dioxolan-4′-yl)pyridazine ( 4 ) by reacting 1,2:5,6-di-O-isopropylidene-3-O-(p-tolylsulfonyl)-α-D-glucofuranose ( 1 ) with hydrazine hydrate via the intermediate 3-deoxy-1,2:5,6-di-O-isopropylidene-α-D-erythro-hex-3-enofuranose ( 3 ) is explained by a mechanism, involving an initial attack of the hydrazine molecule at position 4 in compound 3 , a subsequent ring opening by fission of the C₄? O bond and a ring closure by formation of a N? C₁ bond.     

Synthesis of 3-Deoxy-3-C-Trifluoromethyl-d-Ribose From d-Xylose or d-Glucose

Abstract

The synthesis of 3-deoxy-1,2,O-isopropylidene-3-C-trifluoromethyl-α-D-ribofuranose is described. After a first approach from a commercial D-xylose derivative which was limited by an incomplete stereoselectivity, the synthesis of the title compound was performed from 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose by a reaction sequence where key steps: trifluoromethylation with CF₃SiMe₃ and radical deoxygenation are highly stereoselective.     

Gas Phase Reactions OF 1,2:5,6-DI-O-Isopropylidene-α-D-Gluco- and Allofuranose with Electrophiles Derived From Acetone

ABSTRACT

In a quadrupole mass spectrometer, under chemical ionization conditions with acetone as the reagent gas, 1,2:5,6-di-O-isopropylidene-β-D-glucofuranose and 1,2:5,6-di-O-isopropylidene-β-D-allofuranose form M+1, M+43, and M+59 ions in the gas phase. In addition, the allo isomer produces M+41 ions. These ions and the corresponding ions derived from isotopomers in which the isopropylidene groups were differentiated by deuterium substitution were separately subjected to collisionally activated dissociation conditions. The different reactivities of these ions were attributed to the ability of the allo structure to hydrogen bond internally and the different sizes of the electrophilic groups which formed adducts with the neutral protected sugar molecules.     

Chemical studies of carbohydrates. Part I. Conversion of derivatives of glucose and allose into pyrazoles and pyridazines

On reaction of 1,2:5,6-di-O-isopropylidenc-3-O-(p-tolylsulfonyl)-α-D-glueofuranose ( 1 ) with hydrazine hydrate at 140° besides formation of 3-deoxy-3-hydrazino-1,2:5,6-di-O-isopropylidene-α-D-allofuranose ( 2 ) and 3-dcoxy-1,2:5,6-di-O-isopropylidene-α-D-erythro-hex-3-enofuranose ( 3 ), ring transformation into 3-[4′-(2′,2′-dimethyl-1′,3′-dioxolanyl)]pyridazine ( 4 ) takes place. At 170°, however, only 2 and 4 are formed, indicating that 3 is the precursor of 4. Treatment of 3 with hydrazine hydrate at 170° indeed gives a nearly quantitative ring expansion into 4. Treatment of 3-dcoxy-3-hydrazino-1,2:5,6-di-O-isopropylidenc-α-D-glucofuranose ( 8 ) as well as the stereoisomeric allofuranose 2 with concentrated hydrochloric acid gives a nearly quantitative ring interconversion into 3-(D-erythro-trihydroxypropyl)pyrazole ( 9 ).     

Synthesis of Ether-Linked Di- and Trisaccharide Derivatives Part II- Functionalization and Potential Applications of Ether-Linked Di- and Trisaccharides Containing d-Glucose

Abstract

We have prepared three series of functionalized disaccharides of the type A(6→n)B and a trisaccharide with the formula A-O-B-O-C, in which A = D-glucose (or its derivatives) and both B and C are any of D-fructose, D-galactose, D-glucose, xylitol and glycerol (or their derivatives). These compounds resulted from the regiospecific functionalization of either A or B and either the partial or total deprotection of either 6-O-(3-deoxy-1,2:5,6-di-O-isopropylidene-α-D-glucofuranos-3-yl)-3-O-alkyl-1,2-O-isopropylidene-α-D-glucofuranose or its analogues of type 1 described in part I.¹ We also report results on surface activity and biological properties of some of the molecules prepared.     

Modulation of electronic properties of π‐conjugated copolymers derived from naphtho[1,2‐b:5,6‐b′]dithiophene donor unit: A structure‐property relationship study

A set of three donor‐acceptor conjugated (D‐A) copolymers were designed and synthesized via Stille cross‐coupling reactions with the aim of modulating the optical and electronic properties of a newly emerged naphtho[1,2‐b:5,6‐b′]dithiophene donor unit for polymer solar cell (PSCs) applications. The PTNDTT‐BT , PTNDTT‐BTz , and PTNDTT‐DPP polymers incorporated naphtho[1,2‐b:5,6‐b′]dithiophene ( NDT ) as the donor and 2,2′‐bithiazole ( BTz ), benzo[1,2,5]thiadiazole ( BT ), and pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione ( DPP ), as the acceptor units. A number of experimental techniques such as differential scanning calorimetry, thermogravimetry, UV–vis absorption spectroscopy, cyclic voltammetry, X‐ray diffraction, and atomic force microscopy were used to determine the thermal, optical, electrochemical, and morphological properties of the copolymers. By introducing acceptors of varying electron withdrawing strengths, the optical band gaps of these copolymers were effectively tuned between 1.58 and 1.9 eV and their HOMO and LUMO energy levels were varied between ?5.14 to ?5.26 eV and ?3.13 to ?3.5 eV, respectively. The spin‐coated polymer thin film exhibited p‐channel field‐effect transistor properties with hole mobilities of 2.73 × 10^?3 to 7.9 × 10^?5 cm² V^?1 s^?1. Initial bulk‐heterojunction PSCs fabricated using the copolymers as electron donor materials and [6,6]‐phenyl C71 butyric acid methyl ester (PC₇₁BM) as the acceptor resulted in power conversion efficiencies in the range of 0.67–1.67%. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2948–2958     

Preparation of Primary and Secondary Azidosugars from Diols using the Dioxaphosphorane Methodology

ABSTRACT

Treatment of methyl 2,3-di-O-benzyl-α-D-glucopyranoside (1), methyl 2,3-di-O-acetyl-α-D-glucopyranoside (4), 3-O-benzyl-1,2-O-(1-methylethylidene)-α-D-glucofuranose (6), 3-O-acetyl-1,2-O-(1-methylethylidene)-α-D-glucofuranose (9), 1,2-O-(1-methylethylidene)-α-D-xylofuranose (11) and methyl 2,3-di-O-acetyl-α-D-galactopyranoside (15) with diisopropylazodicarboxylate-triphenylphosphine in tetrahydrofuran led to the corresponding dioxaphosphoranes, which were opened by trimethylsilyl azide affording the silylated primary azidodeoxysugars. When the same reaction was performed on methyl 2,3-di-O-benzyl-α-D-galactopyranoside (20), an inversion of the regioselectivity of the dioxaphosphorane opening was observed, leading mainly to the 4-azido-4-deoxy-α-D-glucopyranoside derivative 27.     

Synthesis and Application of 3,3-Spirocyclopropane Derivatives Obtained from 1,2:5,6-Di-O-Isopropylidene-α-D-Glucofuranose

Abstract

3,3-Spirocyclopropane derivatives (5 and 7) were prepared by three different methods of cyclopropanation starting from 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose (2). Subsequent radical induced cyclopropane ring opening reaction stereo-specifically provided the 3-C-allyl derivative (9). However, activation of the cyclopropyl ring through the aldehyde (10) followed by hydrogenation gave a quaternary chiral derivative (11) which was elaborated to the versatile intermediate (1) by using Bamford-Stevens reaction.

     

A Facile Synthesis of 1,2:3,4:5,6-Tri-O-Isopropylidene-D-Gluconate–A Convenient Precursor of the Open Chain form of D-Glucose

Abstract

Condensation of D-glucono-1,5-lactone (1) with acidified acetone yields in low yield, among other products, 1,2:3,4:5,6-tri-O-isopropylidene-D-gluconate (2).^1,2 Reaction of 2 with sodium methoxide in methanol gives methyl 3,4:5,6-di-O-isopropylidene-D-gluconate³ (3); this compound was prepared recently by Chittenden and co-workers³ directly from 1 (by reaction of 1 with acetone and dimethoxypropane). It is easily transformed³ into 2,3:4,5-di-O-isopropylidene-D-arabinose (4).     

Synthesis of 1,2:5,6-Di-O-isopropylidene-3-O-[3-(5-fluorouracil-1-yl)-propionoyi]-α-D-glucofuranose and its antitumor activity

In order to provide a less toxic 5-fluorouracil derivative, 1,2:5,6-di-O-isopropylidene-3-O-[3-(5-fluorouracill-yl)-propionoyl]-α-D-glucofuranose, which was the derivative of 5-fluorouracil combining indirectly to 3-position of diacetoneglucose, was synthesized, and its antitumor activity was tested.     

A MNDO study of the structural and electronic properties of polysilane model compounds

The results of MNDO geometry optimizations on selected H? (SiH₂)_n? H polysilane model compounds are presented. Near energetic degeneracy is indicated for all-trans(T), alternating gauche–trans (GT), and all-gauche (G⁺G⁺) models (n = 10). The most stable (T) and least stable (G⁺G⁺) conformations are separated by only ca. 0.11 eV. The existence of low-energy barriers to moderate structural distortion is also suggested. Orbital localizations and charge density distributions along the “polymer” backbone are found to be sensitive functions of such distortion. The ground-state electronic distribution of the saturated all-trans silane chains are calculated to be considerably more polarizable than the fully conjugated H? (CH)_n? H π-electron framework of comparable length. The one-electron HOMO → LUMO excitation can be viewed essentially as an in-plane Si 3p → Si3s + H1s intramolecular charge transfer transition. The qualitatively different atomic orbital character of the HOMO and LUMO levels yields transition moment components for the separate repeat units which are relatively small. In the case of the rigidly trans conformation, the phase relationships of the transition moment terms are such as to constructively sum to a large net value reflecting strong optical absorption, as is observed experimentally.     

Novel liquid crystalline organic semiconducting oligomers incorporating N-heterocyclic carbazole moieties for fluorescent OLEDs

A novel class of nematic liquid crystalline organic semiconducting oligomers incorporating N-heterocyclic carbazole moieties has been synthesised using simple and highly efficient reaction pathways. The electroluminescent colour of these novel oligomers can be varied in a controlled manner by molecular design. The values of the ionisation potential and the electron affinity of these electroluminescent oligomers can also be matched by structural design to the Highest Occupied Molecular Orbital (HOMO) energy level of the electron-blocking layer and the Lowest Unoccupied Molecular Orbital (LUMO) energy level of electron-transporting layer in the Organic light emitting diodes to create low charge-injection barriers for electrons and holes, respectively leading to electroluminescence with an efficacy up to 4.1 cd A^?1.     

Highly Thermostable,Non‐oxidizable Indium,Gallium, and Aluminium Perfluorophthalocyanines with n‐Type Character

Perfluorophthalocyanines incorporating three‐valent metals, namely In(Cl), Ga(Cl), and Al(Cl), have been synthesized and characterized. Thermogravimetric analysis revealed that these compounds exhibit outstanding thermal stability and a tendency to sublime at a temperature exceeding around 350 °C without thermal decomposition. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to probe the frontier orbital energy levels of these compounds in THF solution. All three compounds undergo three quasi‐reversible reductions with the first one leading to the formation of an anion radical, namely MPc^?., as confirmed by spectroelectrochemistry. The compounds studied were intrinsically resistive to oxidation, which indicates that they are very good electron acceptors (n‐type materials). The HOMO–LUMO energy gaps (E_g) of the three compounds determined by UV/Vis spectroscopy were relatively unaffected by the three‐valent metals incorporated into the phthalocyanine macrocycle. Similarly, the energies of the HOMO (E_HOMO) and LUMO (E_LUMO) orbitals remained virtually unaffected by the three‐valent metals in the perfluorophthalocyanine. Importantly, all the perfluorophthalocyanines studied possess LUMO levels between ?4.76 and ?4.85 eV, which makes their reduced forms resistant to electron trapping by O₂ and H₂O. This property opens up the possibility for the fabrication of electronic devices operating under ambient conditions. All three compounds demonstrated very good photostability as solid thin films.     

Facile Separation,Spectroscopic Identification,and Electrochemical Properties of Higher Trifluoromethylated Derivatives of [70]Fullerene

We survey the structure and electronic properties of the family of higher trifluoromethylated C₇₀(CF₃)_n molecules with n=14, 16, 18, and 20. Twenty‐two available compounds, of which thirteen are newly obtained and characterized, demonstrate the broad diversity of π‐system topologies, which enabled us to study the interplay between the CF₃ addition pattern and the electronic properties. UV/Vis spectroscopic and cyclic voltammetric studies demonstrate the importance of the exact addition pattern rather than the plain number of addends. Of particular interest is the skew pentagonal pyramid (SPP) addition pattern, which enables formation of closed‐shell cyclopentadienyl anions C₇₀(CF₃)_{n? 1} ^? through CF₃ detachment upon electron transfer. A detailed study of the process is presented for a SPP‐C₇₀(CF₃)₁₆ where potentiostatic electrolysis at the second reduction potential gives C₇₀(CF₃)₁₅^? oxidizable to a persistent C₇₀(CF₃)₁₅^· radical. Together with the literature data for the lower C₇₀(CF₃)_n compounds with n=2–12, the present results show good correlation between the experimental boundary level positions and the DFT predictions. The compounds turn out to be electron acceptor molecular semiconductors with experimental LUMO energies and HOMO–LUMO gaps within the ranges of ?4.3 to ?3.7 eV and 1.6 to 3.3 eV, respectively, depending on the shape of the conjugated fragments. The HOMO levels fall within the range of ?5.6 to ?6.9 eV and show linear correlation with the number of addends.     

Highly Pure Synthesis,Spectral Assignments,and Two‐Photon Properties of Cruciform Porphyrin Pentamers Fused with Benzene Units

Tetrameric porphyrin formation of 2‐hydroxymethylpyrrole fused with porphyrins through a bicyclo[2.2.2]octadiene unit gave bicyclo[2.2.2]octadiene‐fused porphyrin pentamers. Thermal conversion of the pentamers gave fully π‐conjugated cruciform porphyrin pentamers fused with benzene units in quantitative yields. UV/Vis spectra of fully π‐conjugated porphyrin pentamers showed one very strong Q absorption and were quite different from those of usual porphyrins. From TD‐DFT calculations, the HOMO level is 0.49 eV higher than the HOMO?1 level. The LUMO and LUMO+1 levels are very close and are lower by more than 0.27 eV than those of other unoccupied MOs. The strong Q absorption was interpreted as two mutually orthogonal single‐electron transitions (683 nm: 86 %, HOMO→LUMO; 680 nm: 86 %, HOMO→LUMO+1). The two‐photon absorption (TPA) cross section value (σ⁽²⁾) of the benzene‐fused porphyrin pentamer was estimated to be 3900 GM at 1500 nm, which is strongly correlated with a cruciform molecular structure with multidirectional π‐conjugation pathways.     

Thiepin‐Fused Heteroacenes: Simple Synthesis,Unusual Structure,and Semiconductors with Less Anisotropic Behavior

The simple one‐pot syntheses of sulfur‐rich thiepin‐fused heteroacences with an alkylidene–fluorene framework, THA1 and THA6 (thiepin‐fused heteroacene 1 or 6, in which the thiepin is conjugated at both ortho positions with S? CH₃ or S? C₆H₁₃, respectively), is reported. Based on electrochemical studies and theoretical calculations, their LUMO energies are relatively low (?3.26 eV), and their HOMO and HOMO?1 orbitals are nearly degenerate. The thiepin ring contributes mainly to HOMO?1 and LUMO orbitals, however, HOMO orbitals dominantly reside on thienoacence rings. Within the crystal of THA1, the molecules adopt a herringbone arrangement and multiple intermolecular interactions lead to the formation of a 2D network. Interestingly, THA6 shows totally different intermolecular arrangements. Organic field‐effect transistor (OFET) devices show both compounds exhibiting p‐type semiconducting behavior. Thin films or microcrystals of THA1 possess relatively high hole mobility. Moreover, the mobilities of the microcrystal of THA1 along three directions are in the same order, thus the hole‐carrier transporting within the hexagonal‐plane of microcrystal of THA1 exhibits less anisotropic behavior. In comparison, both thin films and microrods of THA6 show low hole mobilities. This agrees well with the intermolecular arrangements and interactions within crystal of THA6. Further theoretical calculations reveal that significant intermolecular electronic coupling among HOMO?1 orbitals and sulfur atoms play an important role in intermolecular electronic coupling for THA1.     

Large branched alkylthienyl bridged naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole-containing low bandgap copolymers: Synthesis and photovoltaic application

Two donor-acceptor (D-A) type low bandgap (LBG) alternating conjugated copolymers containing larger conjugation planarity and stronger electro-withdrawing ability naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT) unit, namely, poly[4,8-bis(5-(n-octylthio)thien-2-yl)-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-4,9-bis(4-(2-decyltetradecyl)thien-2-yl)naphtho- [1,2-c:5,6-c′]bis[1,2,5]thiadiazole-5,5′-diyl] (PBDT-TS-DTNT-DT) and poly[4,8-bis(triiso-propylsilylethynyl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-4,9-bis(4-(2-decyltetradecyl)-thien-2-yl)naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole-5,5′-diyl] (PBDT-TIPS-DTNT-DT), were prepared by the palladium-catalyzed Stille polycondensation and characterized by gel permeation chromatography (GPC), UV-Vis absorption, thermal gravimetric analysis (TGA), cyclic voltammetry (CV) etc. PBDT-TS-DTNT-DT and PBDT-TIPS-DTNT-DT show the broader absorption and deeper highest occupied molecular orbital (HOMO) energy level approximately ?5.45 and ?5.62 eV, respectively. Bulk-heterojuction solar cells based on the resulted polymers and [6,6] phenyl-C₆₁ butyric acid methyl ester (PC₆₁BM) blends, with the device configuration of ITO/PFN/polymer:PC₆₁BM/MoO₃/Ag were prepared and investigated. The results showed the power conversion efficiency (PCE) of 2.67% for PBDT-TS-DTNT-DT/PC₆₁BM (w:w, 1:2) and 0.64% for PBDT-TIPS-DTNT-DT/PC₆₁BM (w:w, 1:1), with relatively high open-circuit voltage (V_OC) of 0.86 and 1.05 V, small short-circuit current (J_SC) of 5.41 and 0.97 mA cm^?2 and moderate fill factor (FF) of 57.8% and 62.4%, under an AM1.5 simulator (100 mWcm^?2), respectively.     

Synthesis and Cation-Binding Properties of (1→6)-2,5-Anhydro-D-glucitol with 3,4-Di-O-Pentyl and Decyl Groups by Cyclopolymerization of 1,2:5,6-Dianhydro-D-mannitols

Abstract

The cyclopolymerizations of 1,2:5,6-dianhydro-3,4-di-O-pentyl-D-mannitol (1b) and 1,2:5,6-dianhydro-3,4-di-O-decyl-D-mannitol (1c) were carried out using BF₃OEt₂ and t-BuOK. All the resulting polymers consisted of cyclic constitutional units, i.e., the extent of cyclization was 100%. The polymer structures for the polymerization with t-BuOK were (1→6)-2,5-anhydro-3,4-di-O-pentyl-D-glucitol (2b) and (1→6)-2,5-anhydro-3,4-di-O-decyl-D-glucitol (2c), whereas those with BF₃O-decyl₂ comprised 2,5-anhydro-D-glucitols as major units along with other cyclic ones. These polymers were soluble in n-hexane, CHCl₃, and THF, but insoluble in water, which differs from the amphiphilic solubility of (1→6)-2,5-anhydro-3,4-di-O-methyl-D-glucitol (2a). The cation-binding properties of 2b and 2c were examined using alkali-metal picrates in order to compare them with those of 2a. The extraction yields for each cation decreased in the order of 2c < 2b < 2a. Every polymer exhibited a similar cation-binding selectivity in the order Cs⁺ > Rb⁺ > K⁺ ? Na⁺ > Li⁺. The ratio of K⁺ and Na⁺, K⁺/Na⁺, was 4.6 for 2a, 5.1 for 2b, and 7.1 for 2c in the increasing order 2a < 2b > 2c.