Strong Electron Acceptor Group Research Articles

Preparation of Novel Push-Pull Benzothiazole Derivatives with Reverse Polarity: Compounds with Potential Non-Linear Optic Application

The hitherto unknown 6-dimethylaminobenzothiazole-2-carbaldehyde was prepared as a starting compound for the synthesis of novel push-pull benzothiazole derivatives with reverse polarity. These compounds are substituted atthe 2-position by strong electron-acceptor groups and at the 6-position by NMe 2 as strong electron-donor. The new method for synthesis of 6-dimethylaminobenzothiazole involved the successful use of sonochemical reductive methylation. Expected non-linear optical properties of target molecules were studied by EFISH method.

Large enhancement of electronic first hyperpolarizability in Donor 1–π–Donor 2 chromophores with charge defects

New strategy in the design of non-linear optical molecular switches has been studied using correlated ab initio methods. The employment of Donor 1–π–Donor 2 chromophores in contrast to the classical Donor–π–Acceptor molecules shows a more efficient modulation of the first hyperpolarizability upon oxidation. This is due to the large enhancement of the first hyperpolarizability obtained in Donor 1–π–Donor 2 chromophores with charge defects, which is about 27 times higher than that of a standard DA chromophore of the same size. This enhancement is explained using electron density derivatives, showing that the introduction of charge defects converts the powerful electron donor group into a strong electron acceptor group.

The effect of the molecular structure of the chromophore on the photorefractive properties of the polymer systems with low glass transition temperatures

Seven chromophores with different dipole moments and polarizability anisotropies were synthesized by varying conjugation bridges, such as polyene, thiophene, indole, and benzene combined with strong electron-donor and electron-acceptor groups. The birefringence of photorefractive materials containing 30 wt% of chromophore was observed to be in the range of 0.45 × 10−3 to 5.0 × 10−3 at an electric field of 70 V µm−1, depending on the chromophore structure. The photorefractive material containing a polyene-based chromophore exhibited the highest photorefractive property, followed by those containing thiophene-based, benzene-based and indole-based chromophores. It was observed that, within material systems used in this study, photorefractive properties of guest–host systems were linearly proportional to the orientational birefringence.

Nonlinear optics. A semiempirical study of organic chromophores

Many donor–acceptor substituted organic compounds show internal charge separation upon excitation. Within this class, the following compounds are studied as suitable candidates for molecules with high second-order nonlinear optical (NLO) response: 4- N, N-dimethylamino-benzonitrile (DMABN), 6-propanoyl-2-(dimethylamino)-naphthalene (PRODAN), and various 4-(4- N, N-dimethylamino-phenyl)-1,3-diphenyl-pyrazolo[3,4-b]quinolines (DMA-DPPQ). The configuration interaction method with single and double excitations (CISD) is used in combination with the sum over states (SOS) approach within the semiempirical AM1 parametrization to calculate the vector component of the hyperpolarizability along the dipole axis β μ . The influence of changing molecular geometry on the second-order nonlinear properties is calculated for various intramolecular relaxation coordinates. Solvent effects are explicitly studied for DMABN by a self-consistent reaction field (SCRF) model revealing an increasing NLO-effect with increasing solvent polarity. The hyperpolarizability is discussed in relationship to the charge transfer properties of the excited state. The calculated values are in good agreement with experimental data for both DMABN and PRODAN. DMA-DPPQ is found to be a good NLO chromophore only when increasing either the donor or acceptor strength. Its nonlinear response can be drastically increased by an additional strong electron acceptor group, e.g. a NO 2-group, at the primary acceptor moiety.

A Molecular Orbital Study on the Optical Properties of Fluorescent Dyes

ABSTRACTFluorescent dyes including Nile Red (NR), fluorescein, rhodamine and 4- (dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) derivatives were investigated to find an application for the organic light emitting device (OLED). Relationship between the molecular structure and optical property was calculated by ab initio (HF and DFT/6-31G*) and semiempirical (AM1/PM3 and INDO/S) calculation methods for the geometry optimization and for the information of electronic transition, respectively. The absorption maximum and the oscillator strength of molecules strongly depended on the molecular dipole moment, especially for the molecules having both strong electron donor and acceptor group. Since the calculated results were comparable with several experimental results, these semiempirical molecular orbital calculation methods could be used as a powerful prediction tool for optical properties of the luminescent molecules.

Alternating Donor−Acceptor Substitutions in Conjugated Polythiophenes

A series of bithiophenes, disubstituted with electron donor and electron acceptor groups, have been synthesized. The electronic effects exerted by these groups, on the electrochemical oxidation potential of bithiophenes, are additive, which allows us to control the overall substituent effect and make it compatible with the electropolymerization of these molecules. The electrochemical characterization of the resulting polymers has revealed unusual properties, in the case of unsymmetrical disubstitution with strong electron acceptor and donor groups. Charge confinement is observed for the first oxidated state of poly(3-cyano-3‘-methoxybithiophene), which has been interpreted by the existence of multiple potential wells, created by these push−pull substituents alternating along the conjuated polythiophene chain.

Intramolecular charge transfer and exciplex formation in anthracene bichromophoric compounds

A binary compound containing strong electron donor and acceptor groups, ( N,N-dimethylanilino)-CH 2-9-cyanothrace ne ( II), was synthesized, and its photophysical behaviour was studied. Intramolecular exciplex emission was observed in non-polar and moderately polar solvents, but not in polar solvents. Exciplex formation in non-polar and moderately polar solvents accounts for the exothermic electron transfer reaction and/or the efficient coupling of the amine lone pair with 9-cyanoanthracene π orbitals; in polar solvents, the molecular structure corresponds to a solvent-separated radical ion pair formed by intermolecular electron transfer, where the energy is dissipated via back electron transfer (BET) without fluorescence emission. A new, blue-shifted emission at 510 nm appears in the region of the local emission band for compound II at 77 K, which may originate from a ground state, charge transfer (CT) conformer. The dependence of exciplex formation on the solvent and temperature is discussed by comparison with the compound ( N,N-dimethylanilino)-CH 2-anthracene ( I), and a simplified energy diagram showing intramolecular charge transfer and exciplex formation in compounds I and II is described. energy diagram showing intramlecular charge transfer and exciplex formation in compounds I and II is described.

Influence of substituents in salicylaldehyde molecule on interaction with 2-imino-3,5-dimethylthiazolidine

Salicylaldehyde, 5-chlorosalicylaldehyde, or o-vanillin will react with 2-imino-3,5-dimethylthiazolidine to form previously unknown bis(3,5-dimethylthiazolidin-2-ylideneamino)-2-hydroxyphenylmethanes. If strong electron-acceptor groups are present on the aromatic ring, an acid-base interaction takes place. Thus, 3-nitro-5-methoxy-, 3-nitro-5-chloro-, and 3-bromo-5-nitrosalicylaldehyde react with the heterocyclic base to form saltlike complexes, the structure of which has been confirmed by x-ray diffraction.

Vibrational spectroscopy and conformations of 2,2-diacylethenamines

The i.r., Raman, and 1H n.m.r. spectra of 2,2-diacetylethenamines (3) and 2-aminomethylene-5,5-dimethylcyclohexane-1,3-diones (4) show that these substances exist exclusively in the chelated enamino-diketone form, and that the conjugated system contained in them is essentially planar. The open-chain enamino-diketones (3) exist either in the solid state or in solution in the EZE-conformation (7). A similar conjugated core, having the fixed ZZE-conformation, contained in 5-aminomethylene-2,2-dimethyl-1,3-dioxane-4,6-diones (5) is most probably planar or nearly planar. The EZE- and ZZE- alignments of the enamino-diketones can be distinguished by their spectral properties, and particularly, by their vibrational spectra. Some features of the i.r. and Raman spectra indicate vibrational coupling between the two ν(CO) vibrations, the effect being more marked in the cyclic enamino-diketones (4) and -diesters (5) than in their open-chain analogues. On the other hand, the coupling of the ν(CO) with the ν(CC) and the δ(N–H) modes seems to be less efficient in these enaminodione systems than in the related simple enaninones. Further arguments are presented questioning the criteria established to ascertain the planarity of enamino-diones and of other enamines having two strong electron-acceptor groups at C-2.

Chiral differentiation by the P-(+)-hexahelicene-7,7′-dicarboxylic acid disodium salt. Resolution of N-2,4-dinitrophenyl-α-amino-acid esters by high performance liquid chromatography

Derivatives of α- amino-acid esters containing a strong electron acceptor group, were resolved on silica gel coated with a chiral electron donor substance.