Electron-donating Methyl Research Articles

Reactions of 4-substituted 5 H-1,2,3-dithiazoles with primary and secondary amines: fast and convenient synthesis of 1,2,5-thiadiazoles, 2-iminothioacetamides and 2-oxoacetamides

The treatment of 5 H-1,2,3-dithiazole-5-thiones 1 in chloroform under reflux and 5 H-1,2,3-dithiazol-5-ones 2 in THF at room temperature with primary aliphatic amines and benzylamine afforded 1,2,5-thiadiazole-3(2 H)-thiones 3 and 1,2,5-thiadiazol-3(2 H)-ones 6, respectively. The structure of dithiazolone 3f was confirmed by X-ray diffraction analysis. The reaction of dithiazolone 2e bearing an electron-donating methyl group in the 4-position gave 2-oxoacetamide 7e in high yield. The reaction of thiones 1 with secondary aliphatic amines in DMSO yielded 2-iminothioacetamides 8 in moderate yields together with elemental sulfur. Interestingly, the treatment of dithiazolones 2 with secondary amines under the same conditions afforded 2-oxoacetamides 9—the products of the hydrolysis of corresponding imino derivatives 10, which was isolated as 10b. A general mechanism was proposed for the formation of the products.

Design of a Potent and Selective Small Molecule Kv1.5 Blocker

The voltage-gated potassium channel Kv1.5 is being studied extensively as a potential target for treating atrial fibrillation and other life-threatening arrhythmias. Since Kv1.5 is expressed selectively in the human atrium and not in the ventricle, a potent and selective Kv1.5 blocker should therefore significantly increase the action potential duration (APD) of the atrium without affecting that of the ventricle. Unlike the existing anti-arrhythmic drugs such as amiodarone, sotalol etc. that block the Kv11.1 channel (hERG), a potent and selective Kv1.5 blocker should not induce dangerous and fatal proventricular arrhythmia.Phenoxyalkoxypsoralens (PAPs) are a class of compounds that has previously been described to block both the lymphocyte Kv1.3 and the cardiac Kv1.5 channel (Mol. Pharmacol. 2005). Through a combination of classical medicinal chemistry and traditional electrophysiology, we now studied the structure-activity relationship of PAPs with the aim of generating more selective Kv1.5 blockers. When the side chain phenyl ring of PAPs were decorated with a combination of electron-donating (methyl) and electron-withdrawing (nitro) groups as in PAP-22 {5-[3-(4-methyl-2-nitrophenoxy)-propoxy]psoralen}, the compounds exhibited a four to five fold increase in selectivity for Kv1.5 over Kv1.3. However, when we substituted the nitro group with a chloro group, as in PAP-25 {5-[2-chloro-4-methylphenoxy)propoxy]-psoralen}, more selective Kv1.3 blockers were generated. We are currently further investigating the effect of other strongly electron-withdrawing groups instead of the nitro group in order to increase the potency and selectivity of PAPs for Kv1.5 over Kv1.3. Other fused tricyclic rings containing 2-aminobenzothiazole are also being explored as a potential pharmacophore to design and develop Kv1.5 blockers.Supported by The Board of Regents Support Fund

Structures and Spin States of Bis(tridentate)-Type Mononuclear and Triple Helicate Dinuclear Iron(II) Complexes of Imidazole-4-carbaldehyde azine

Mononuclear [Fe(H(2)L(R))(2)](2+) and dinuclear [Fe(2)(H(2)L(R))(3)](4+) (R = H, 2-Me, 5-Me) complexes containing the new imidazole-4-carbaldehyde azine ligand (H(2)L(H)) and its derivatives (H(2)L(2-Me) and H(2)L(5-Me)) prepared from the condensation reaction of 4-formylimidazole or 2-methyl- or 5-methyl-4-formylimidazole with hydrazine (2:1) were prepared, and their magnetostructural relationships were studied. In the mononuclear complexes, H(2)L(R) acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom, while in the dinuclear complexes, H(2)L(R) acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate. At room temperature, [Fe(2)(H(2)L(H))(3)](ClO(4))(4) and [Fe(2)(H(2)L(2-Me))(3)](ClO(4))(4) were in the high-spin (HS) and low-spin (LS) states, respectively. The results are in accordance with the ligand field strength of H(2)L(2-Me) with electron-donating methyl groups being stronger than H(2)L(H), with the order of the ligand field strengths being H(2)L(2-Me) > H(2)L(H). However, in the mononuclear [Fe(H(2)L(H))(2)](ClO(4))(2) and [Fe(H(2)L(2-Me))(2)](ClO(4))(2) complexes, a different order of ligand field strengths, H(2)L(H) > H(2)L(2-Me), was observed because [Fe(H(2)L(H))(2)](ClO(4))(2) was in the LS state while [Fe(H(2)L(2-Me))(2)](ClO(4))(2) was in the HS state at room temperature. X-ray structural studies revealed that the interligand steric repulsion between a methyl group of an H(2)L(2-Me) ligand and the other ligand in [Fe(H(2)L(2-Me))(2)](ClO(4))(2) is responsible for the observed change in the spin state. Two kinds of crystals, needles and blocks, were isolated for [Fe(2)(H(2)L(H))(3)](BF(4))(4), and both exhibited a sharp spin transition, [LS-HS] <--> [HS-HS]. The spin transition of the block crystals is more abrupt with a hysteresis, T(c) upward arrow = 190 K and T(c) downward arrow = 183 K with DeltaT = 7 K.

The Role of Ancillary Ligands in Iridium(III) Complexes for Blue OLEDs

In this study, new deep blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other and two cis-ancillary ligands, such as Ir{(CF3)2Meppy}(PPh3)2(H)(Cl), [Ir{(CF3)2Meppy}(PPh3)2(H)(NCMe)]+ and Ir{(CF3)2Meppy} (PPh3)2(H)(CN), [(CF3)2Meppy = 2-(3′,5′-bis-trifluoromethylphenyl)-4-methylpyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. We investigate the strong field capabilities of ancillary ligands to gain insight into the factors responsible for the emission color change and the different luminescence efficiencies. This work represents a strategy for the design of deep blue phosphorescent iridium complexes. The electron-withdrawing trifluoromethyl group substituted on the phenyl ring, the electron-donating methyl group on the pyridyl ring and the cyano strong field ancillary ligand increase HOMO-LUMO gap to achieve the hypsochromic shift in emission color. As a result, the maximum emission spectrum of Ir{(CF3)2Meppy}(PPh3)2(H)(Cl), [Ir{(CF3)2Meppy}(PPh3)2(H)(NCMe)]+ and Ir{(CF3)2Meppy}(PPh3)2(H)(CN) were in the ranges of 436, 434 and 434 nm, respectively.

Molecular-shape selectivity tuned by donor–acceptor type copolymers as organic phase in reversed-phase high-performance liquid chromatography

The copolymer with a terminal reactive group (copoly-VP 17 MA 12 ) was newly designed and prepared by selecting 4-vinylpyridine (VP) as an electron-donating monomer and methyl acrylate (MA) as an electron-accepting monomer. Copoly-VP 17 MA 12 was grafted onto porous silica particles by a silanol coupling reaction with the terminal group. Individually, poly-VP 15 and poly-MA 20 with a terminal reactive group were also synthesized and co-grafted onto silica (Sil-cograft-VP 15 MA 20 ) to compare the effect of the copolymer-grafted (Sil-copoly-VP 17 MA 12 ) and polymer co-grafted stationary phases in HPLC separation. All the polymers were characterized by 1H NMR and FT-IR analysis before grafting on silica. Polymer grafting was confirmed by diffuse reflectance infrared Fourier transform (DRIFT), elemental analysis and thermogravimetric analysis (TGA). The intra- and intermolecular interaction between monomer units in copolymer-grafted and polymer co-grafted systems, respectively was observed by DRIFT measurement. The detailed chromatographic study revealed using PAHs as solutes that remarkably higher selectivity for planar/non-planar discrimination was observed with the copolymer-grafted phase than with the co-grafted stationary phase. In this paper, it is also discussed that the selectivity enhancement by copolymer-grafting in the Sil-copoly-VP 17 MA 12 phase can be brought through intramolecular interaction between VP and MA.

Achieving blue luminescence of Alq 3 through the pull-push effect of the electron-withdrawing and electron-donating substituents

A novel blue-emissive Alq 3 derivative, tris-(4-methyl-6-fluoro-8-hydroxyquinoline) aluminum ( 6), has been designed and prepared. Because the strong electronegative F atom at 6-position lowers the HOMO significantly and the weak electron-donating methyl group at 4-position retains the drop of the LUMO, the band gap of 6 is broadened, and a blue-shift by 53 nm of the emission peak ( λ em ) with substantially enhanced intensity is demonstrated when compared to that of Alq 3. It is also found that 6 possesses good thermal stability and solubility in common solvents. Through theoretical simulations of the frontier orbitals, it is disclosed that 6's λ em can be blue-shifted further if methyl is replaced with a stronger electron-donating substituent, such as methoxy or N, N′-dimethylamino group.

Design, synthesis, spectral analysis and in vitro microbiological evaluation of 2-phenyl-3-(4,6-diarylpyrimidin-2-yl)thiazolidin-4-ones

A series of novel 2-phenyl-3-(4,6-diarylpyrimidin-2-yl)thiazolidin-4-ones 23-33 were synthesized, and studied for their in vitro antibacterial and antifungal activities against clinically isolated strains. Generally compounds possessing electron donating groups showed good antibacterial activity. Compound 31, which contain both electron withdrawing chloro and electron donating methyl groups showed potent activity against all the tested Gram positive and Gram negative bacterial strains whereas compounds 32 and 33 which contain electron donating methoxy functional group at the para position of the phenyl ring attached to pyrimidine ring showed promising activity against S.aureus, S.typhii and E.coli. Compounds 32 and 33, both containing electron withdrawing groups (-Cl, -F) showed excellent activities against all the tested A. flavus, Mucor, Rhizopus and M.gypsuem fungal strains. while against Mucor, compound 27 which contains an electron donating methyl group at the para position of the phenyl ring attached to pyrimidine ring showed promising activity. Also compound 31, which contains both electron withdrawing chloro and electron donating methyl groups showed potent activity against A. flavus and Rhizopus.

Electrochemical investigations of oxovanadium(IV) complexes with bidentate Schiff base ligands in dimethylformamide

1, VO(sal-tod) 2 2, VO(hmp-and) 2 3 and VO(hmp-oxime) 2 4 have been studied in DMF/0.1 M TBAP using cyclic voltammetry at a Pt-working electrode. The electrochemistry of sal-anl and sal-tod ligands was also examined for the sake of comparison. Complexes 1 and 2 show almost similar electrochemistry. Oxidation of complex 2 is easier while reduction is difficult in comparison to 1 due to the +I inductive effect of electron-donating methyl group at the para position of toluidine. Complex 1 showed two irreversible anodic waves at E Pa1 = +0.68 V and E Pa2 = +1.06 V vs SCE and two irreversible cathodic peaks at E pc , 1 = -0.90 V and E pc2 = -1.325 V vs SCE followed by an irreversible anodic peak at E pa'2 = -0.42 V at scan rate 100 mV s -1 . On the basis of CV results, it is concluded that in complexes 1 and 2, the redox processes a 1 and c 2 are metal-based while the redox processes a 2 and c 1 ' seem to be ligand-based. The CVs of 3 and 4 are also qualitatively similar. It is noteworthy that the anodic peak potential for the process VO 2+/3+ shifted to more positive values in the sequence: VO(sal-tod) 2 → VO(sal-anl) 2 → VO(hmp-oxime) 2 → VO(hmp-and) 2 .

Intramolecular alkoxide-tethered permethyltitanocene(III) complexes – synthesis and crystal structure

Singly tucked-in titanocene [Ti(III)(η5-C5Me5)(η5:η1-C5Me4CH2)] (1) reacted readily with di-tert-butyl ketone and 2,4,6-trimethylacetophenone to give permethyltitanocene derivatives [Ti(III)(η5-C5Me5){η5-C5Me4CH2C(t-Bu)2O-κO}] (2) and [(Ti(III)(η5-C5Me5)-{η5-C5Me4CH2CMe(C6H2Me3)O-κO}] (3) with the tetramethylcyclopentadienyl ring tethered to the titanium atom by ethoxy group disubstituted at Cα. Crystal structures of 2 and 3 showed that the Ti–O bond is only slightly inclined to the tethered cyclopentadienyl ligand, and the bulky mesityl or tert-butyl substituents did not impose an observable steric hindrance into molecules of 2 and 3. Whereas the Ti–O bond lengths in 2 and 3 do not significantly differ, a higher wavenumber of the 1a1 → b2 electronic transition for 2 (7326 cm–1) compared with that for 3 (6666 cm–1) indicates a more efficient oxygen-to-titanium π-electron back donation in 2. This is induced by two electron-donating tert-butyl groups on Cα compared with a combined effect of electron-donating methyl and electron-attracting mesityl substituents in 3.

Photoluminescence and electroluminescence by gallium(III) complexes of N-salicylidene-o-aminophenol and its derivatives

N-salicylidene-o-aminophenol and two of its derivatives bearing either an electron-donating methyl group or an electron-withdrawing Br group were used as ligands for the synthesis of three Ga(III) complexes. The complexes involved the participation of one acetylacetonate and one ethanol or methanol molecule. The geometry of the dianion of the Schiff base in the complexes is planar while photoluminescence data showed that photoluminescence intensity was extensively increased upon complex formation. Complexes emitted ligand-centered luminescence by ligand-centered excitation. Substituent groups broadly modified emission maximum. These substitutions can be exploited to tune light emission by the complex. All three complexes were used for the construction of electroluminescence devices and all emitted electroluminescence. Both photoluminescence and electroluminescence emission was enhanced in the case of substituted Schiff bases.

Reactions of Hydrated Electrons with Pyridinium Salts in Aqueous Solutions

Rate coefficients for the reactions of the hydrated electron (e(aq)(-)) with pyridinium salts in aqueous solutions have been determined using pulse radiolysis techniques. The rate coefficients for pyridine, 1-hydropyridinium chloride, and 1-hydropyridinium nitrate were observed to be 1.4 x 10(10), 4.5 x 10(10), and 5.3 x 10(10) M(-1) s(-1), respectively. The e(aq)(-) was found to primarily attack the pyridine ring, the proton coordinated to the nitrogen atom, and the nitrate counterion, but not the chloride. Results for the corresponding dimer structures of 4,4'-dipyridyl, 1,1'-dihydro-4,4'-bipyridinium dichloride, and 1,1'-dihydro-4,4'-bipyridinium dinitrate had similar trends for e(aq)(-) attack sites. The rate coefficients for pyridinium salts were lower when the pyridinium nitrogen atom is coordinated to a methyl group rather than to a proton. This reduction is probably due to the increase in electron density of the pyridine ring due to the electron-donating methyl group. Pyridinium salts are not major contributors to the production of molecular hydrogen in the radiolysis of aqueous solutions and actually decrease molecular hydrogen yield due to scavenging reactions of the e(aq)(-). The yield of molecular hydrogen decreases from 0.45 to approximately 0.2 molecule/(100 eV) over the scavenging capacity range for the e(aq)(-) of 10(5)-10(9) s(-1). Absorption spectra of the transient species produced by the reactions of pyridinium salts with OH radical and H atom formed in water radiolysis were observed, and rate coefficients for these reactions were determined.

Theoretical Study of Solvent and Substituent Effects on the Reactions of 1,4-Benzoquinone with Cyclopentadiene and Cyclohexadiene

Ab initio quantum mechanics and ONIOM calculations were used to study solvent and substituent effects on the reactions of 1,4-benzoquinone with cyclopentadiene and cyclohexadiene derivatives in tetrahydrofuran and greater water solvents. These calculations revealed (i) that increasing the number of electron donating methyl group substituents and (ii) the proximity of substituents to the reacting carbons (carbon atoms which contribute to the forming C—C bonds) on the diene, promote charge transfer from the diene to the dienophile in the transition state. These effects increase the negative charge on the oxygen atoms, destabilize the transition state in the organic solvent by increasing steric interactions, and stabilize the transition state in water solvent by increasing the strength of hydrogen bonding. These results, along with consideration of variations in the solvent-accessible surface area (SASA) confirmed that the dramatic acceleration in the rate of the studied reactions in water solvent arise in part from hydrophobic association of the reactants, but predominantly arise from hydrogen bonding between water molecules and the polarized transition state.

Influence of type and positioning of N-aryl substituents on vinyl polymerization of norbornene by Ni(II) α-diimine complexes

Effects of structural variations of the diimine ligand on catalyst activities for vinyl polymerization of norbornene (NB) have been investigated by a series of Ni(II) α-diimine catalysts of the general formula: [{ArN=C(Ac)-C(Ac)=NAr}]NiBr2 (Ac=acenaphthyl) (Cat(H), Ar=C6H5; Cat(2,6-Me), Ar=2,6-C6H3Me2; Cat(2,6-Et), Ar=2,6-C6H3Et2; Cat(2,6- i Pr), Ar=2,6-C6H3 i-Pr2; Cat(2,3-Me), Ar=2,3-C6H3Me2; Cat(2,4-Me), Ar=2,4-C6H3Me2; Cat(2,5-Me), Ar=2,5-C6H3Me2; Cat(3,5-Me), Ar=3,5-C6H3Me2; Cat(2,4,6-Me), Ar=2,4,6-C6H2Me3). In situ reactions with methylaluminoxane generated the active catalysts, and they showed good activity towards NB polymerizations. As indicated by relatively higher activities of Cat(H) and Cat(3,5-Me), it can be generalized that catalysts having 2,6-substituents are less active due to steric interaction between monomer and substituents. In addition, electron donating methyl groups at 2-, 4-or 6-position on the N-aryl have a con effect and that at 3,5-position has a pro effect.

PL and EL properties of oligo( p-phenylene vinylene) (OPPV) derivatives and their applications in organic light-emitting diodes (OLED)

This paper reports the photoluminescence properties and the performance enhancement of organic light-emitting diodes (OLEDs) of a series of well-defined π-conjugated rigid rod oligomers analogous to poly( p-phenylenevinylene) (PPV). They are based on benzene-1,4-bis(phenylene vinylene) (OPPV) with electron-withdrawing (nitro) or electron-donating (methyl and dimethylamino) substituents in para-position of the terminal rings of the molecule. Substitution with methoxy and a long alkoxy group (hexadecyloxy) in 2,5-positions is also examined. Photoluminescence spectra obtained from films are discussed and compared to those previously reported in tetrahydrofuran solutions. OPPV oligomers were then used as emissive material in OLEDs and the I– V– L characteristics of the devices are presented. The results show that donating groups placed on the OPPV backbone increases the performances of the devices.

Sulfur X-ray Absorption and Vibrational Spectroscopic Study of Sulfur Dioxide, Sulfite, and Sulfonate Solutions and of the Substituted Sulfonate Ions X3CSO3- (X = H, Cl, F)

Sulfur K-edge X-ray absorption near-edge structure (XANES) spectra have been recorded and the S(1s) electron excitations evaluated by means of density functional theory-transition potential (DFT-TP) calculations to provide insight into the coordination, bonding, and electronic structure. The XANES spectra for the various species in sulfur dioxide and aqueous sodium sulfite solutions show considerable differences at different pH values in the environmentally important sulfite(IV) system. In strongly acidic (pH < approximately 1) aqueous sulfite solution the XANES spectra confirm that the hydrated sulfur dioxide molecule, SO2(aq), dominates. The theoretical spectra are consistent with an OSO angle of approximately 119 degrees in gas phase and acetonitrile solution, while in aqueous solution hydrogen bonding reduces the angle to approximately 116 degrees . The hydration affects the XANES spectra also for the sulfite ion, SO32-. At intermediate pH ( approximately 4) the two coordination isomers, the sulfonate (HSO3-) and hydrogen sulfite (SO3H-) ions with the hydrogen atom coordinated to sulfur and oxygen, respectively, could be distinguished with the ratio HSO3-:SO3H- about 0.28:0.72 at 298 K. The relative amount of HSO3- increased with increasing temperature in the investigated range from 275 to 343 K. XANES spectra of sulfonate, methanesulfonate, trichloromethanesulfonate, and trifluoromethanesulfonate compounds, all with closely similar S-O bond distances in tetrahedral configuration around the sulfur atom, were interpreted by DFT-TP computations. The energy of their main electronic transition from the sulfur K-shell is about 2478 eV. The additional absorption features are similar when a hydrogen atom or an electron-donating methyl group is bonded to the -SO3 group. Significant changes occur for the electronegative trichloromethyl (Cl3C-) and trifluoromethyl (F3C-) groups, which strongly affect the distribution especially of the pi electrons around the sulfur atom. The S-D bond distance 1.38(2) A was obtained for the deuterated sulfonate (DSO3-) ion by Rietveld analysis of neutron powder diffraction data of CsDSO3. Raman and infrared absorption spectra of the CsHSO3, CsDSO3, H3CSO3Na, and Cl3CSO3Na.H2O compounds and Raman spectra of the sulfite solutions have been interpreted by normal coordinate calculations. The C-S stretching force constant for the trichloromethanesulfonate ion obtains an anomalously low value due to steric repulsion between the Cl3C- and -SO3 groups. The S-O stretching force constants were correlated with corresponding S-O bond distances for several oxosulfur species.

Catalytic air oxidation of olefins using molybdenum dioxo complexes with dissymmetric tridentate O,N,S-donor Schiff base ligands derived from o-hydroxyacetophenone and S-benzyldithiocarbazate or S-methyldithiocarbazate

We report the homogeneous catalytic air oxidation of 1-hexene, cyclohexene and styrene using cis-[MoO 2(hap-SBDTC)(solv)] ( 1b) and cis-[MoO 2(hap-SMDTC)(solv)] ( 2b), where hap-SBDTC and hap-SMDTC are Schiff bases derived from o-hydroxyacetophenone (hap) and S-benzyldithiocarbazate (SBDTC) or S-methyldithiocarbazate (SMDTC), respectively. Both hap-SBDTC and hap-SMDTC are dissymmetric tridentate O,N,S-donor Schiff base ligands. The catalytic tests were performed in DMF solvent at 60 °C under 1 atm O 2.The olefin conversion was determined using gas chromatography. The percentage conversion of the above-mentioned substrates at the end of 6 h was in the range 86–98%. The final oxidation products were found to be 1-hexanal for 1-hexene, styrene epoxide and phenyl acetaldehyde (81:19) for styrene and cyclohexene epoxide and 2-cyclohexen-1-ol (85:15) in the case of cyclohexene. The oxidation reaction typically followed pseudo-order kinetics; however, a two-stage first order reaction is evident with complex 2b. This is attributed to less steric and electron-donating methyl substitution on S in 2b that possibly imparted a higher reactivity accompanying the formation of an intermediate in a relatively faster reaction step prior to the formation of final oxidation products. A reaction mechanism that explains the experimental results is proposed.

N-(3-Chlorophenyl)methanesulfonamide

The conformation of the N—H bond in the structure of the title compound (3CPMSA), C7H8ClNO2S, is neither syn nor anti to the meta-chloro substituent, in contrast to the anti conformations observed for the stronger electron-withdrawing meta-nitro substituted (3NPMSA) and electron-donating meta-methyl substituted compounds (3MPMSA). The substitution of the Cl atom at the meta position of N-(phen­yl)-methane­sulfonamde (PMSA) changes its space group from P21/c to C2/c compared to the change over from monoclinic P21/c to ortho­rhom­bic Pccn on meta-substitution of the electron-donating methyl group in PMSA and from monoclinic P21/c to triclinic P\overline{1}, on meta-substitution of the stronger electron-withdrawing nitro group. The bond parameters in PMSA, 3CPMSA, 3MPMSA and 3NPMSA are similar except for some differences in the S—N—C—C torsion angles. As in other alkyl sulfonanilides, the amide hydrogen is available to a receptor mol­ecule during its biological activity, as it sits alone on one side of the plane of the benzene ring, while the whole methane­sulfonyl group is on the opposite side of the plane. The mol­ecules in the title compound are packed into chains in the b-axis direction via N—H⋯O hydrogen bonds [H⋯O = 2.06, N⋯O = 2.979 (3) Å and N—H⋯O 169°].

Characterization of model luminescent PPV analogues with donating or withdrawing groups

Several oligomers analogous to poly(p-phenylene vinylene) (PPV) were synthesised by the Wittig reaction, to be used as model compounds for the study of structure/properties relationship. They are based on benzene-1,4-bis(phenylene vinylene) (OPPV) substituted by electron-withdrawing (nitro) or electron-donating (methyl and dimethylamino) groups on the terminal rings of the molecule. Moreover, two other oligomers 2-hexadecyloxy-5-methoxybenzene-1,4-bis(phenylene vinylene) (1-16-OPPV) and 2-hexadecyloxy-5-methoxybenzene-1,4-bis(4-dimethylaminophenylene vinylene) (1-16-NC-OPPV) were prepared with alkoxy groups on the central ring of the molecule. After a complete structural characterization by FTIR, 1H and 13C NMR, particular emphasis was placed upon the investigation of their thermal stability by TGA and their optical properties in tetrahydrofuran (THF) solutions. Depending on the substituent and on its position in the molecule a different thermal behaviour was observed. Moreover, a red-shift from 10 to 50nm was observed for the emission wavelength, with respect to unsubstituted OPPV. Several model compounds (with donating groups) exhibited high fluorescence quantum yields, from 51% to 68%. On the other hand, a very low yield was obtained for the oligomer with nitro groups, that was explained from semi-empirical calculations. These results showed promising properties for the incorporation of these oligomers in electroluminescent diodes.

Cyclic voltammetric studies of some bis(phenanthrolines)copper(II) complexes

The electrochemical properties of some bis(phenanthrolines)copper(II) complexes, [Cu(NN) 2 ](ClO 4 ) 2 (NN denotes 1,10-phenanthroline (phen); 4,7-diphenyl-1,10-phenanthroline (bathophen); 2,9-dimethyl-1,10-phenanthroline (dmp) and 2,9-diphenyl-1,10-phenanthroline (dpp) have been studied by cyclic voltammetry at a platinum working electrode in dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) containing 0.1 M tetrabutyl ammonium perchlorate (TBAP) as the supporting electrolyte. All these complexes display a quasireversible Cu 2+/+ redox couple. Both the electron-donating methyl groups and electron-withdrawing phenyl groups at the 2,9-positions of the phen ligand elevate the Cu 2+/+ redox potentials of the [Cu(dmp) 2 ](ClO 4 ) 2 and [Cu(dpp) 2 ](ClO 4 ) 2 complexes. The redox potentials of [Cu(dmp) 2 ] 2+ are nearly 50 mV more positive than that of [Cu(dpp) 2 )] 2+ in a given solvent. It is found that the Cu 2+/+ reduction potential (E pc ) as well as formal potential (E 0' ) for a given complex all shifted to more positive values in DMF as compared to that in DMSO.

Substituents on Quinone Methides Strongly Modulate Formation and Stability of Their Nucleophilic Adducts

Electronic perturbation of quinone methides (QM) greatly influences their stability and in turn alters the kinetics and product profile of QM reaction with deoxynucleosides. Consistent with the electron-deficient nature of this reactive intermediate, electron-donating substituents are stabilizing and electron-withdrawing substituents are destabilizing. For example, a dC N3-QM adduct is made stable over the course of observation (7 days) by the presence of an electron-withdrawing ester group that inhibits QM regeneration. Conversely, a related adduct with an electron-donating methyl group is very labile and regenerates its QM with a half-life of approximately 5 h. The generality of these effects is demonstrated with a series of alternative quinone methide precursors (QMP) containing a variety of substituents attached at different positions with respect to the exocyclic methylene. The rates of nucleophilic addition to substituted QMs measured by laser flash photolysis similarly span 5 orders of magnitude with electron-rich species reacting most slowly and electron-deficient species reacting most quickly. The reversibility of QM reaction can now be predictably adjusted for any desired application.