Intramolecular Charge Transfer Compounds Research Articles

Luminescence and photoconductivity of poly-n-epoxypropylcarbazole with intramolecular charge transfer compounds

Luminescence and photoconductivity of poly-n-epoxypropylcarbazole with intramolecular charge transfer compounds

Evaluation ofin vitro stability of small unilamellar vesicles coated with collagen and chitosan

To improve the in vitro stability of small unilamellar vesicles (SUV), the permeability of SUV, made from soyabean phosphatidylcholine (PC) and coated with collagen and chitosan, was studied using 5(6)-carboxyfluorescein (5(6)-CF) as a fluorescence probe. The results showed that the coating with a collagen/PC weight ratio of 2, or a chitosan/PC weight ratio of 8, significantly decreased the permeability of liposomal membranes. In addition, the fluorescence polarization method was used to study the influence of a coating with collagen and chitosan at the above ratios on the fluidity of liposomal membranes, employing an intramolecular charge transfer compound, a 3-methoxy-4′-N ,N-dimethylaminoflavone derivative (DMMF), as a fluorescence probe. The fluidity of a liposomal membrane coated with either of the two macromolecules showed no obvious changes, indicating that SUV coated with collagen and chitosan at appropriate weight ratios, can significantly improve the in vitro stability of liposomal membranes without disturbing their fluidity. © 1999 Society of Chemical Industry

Electronic Characterization of Nonlinear Optically Active 8,8-Dicyano-3-(4‘-N,N-dimethylamino)phenylheptafulvene

Some new 8,8-dicyanoheptafulvene derivatives have been synthesized, among which the title compound (1a) is found to crystallize in the polar space group of P1 showing nonlinear optical characteristics. The molecule is composed of a strong acceptor of the dicyanomethylidene group and a strong donor of the dimethylamino group, both of which are combined with the π-conjugated heptafulvene skeleton. Compound 1a is therefore typical of an intramolecular charge transfer compound, for which a high second-order hyperpolarizability is expected. For this reason, the electronic structure has been investigated in solution and in the solid state on the basis of the molecular and crystal structures together with molecular orbital calculations. The solid-state spectrum is found to be strikingly different from the solution spectrum because of the difference in effective conjugation between the seven-membered ring and phenyl ring. There are two electronic transitions A (about 450 nm) and B (580−650 nm) in the solid. Band A is due mainly to the 8,8-dicyanoheptafulvene skeleton, while band B is of charge-transfer character due to the dicyanomethylidene and dimethylamino groups.

The aggregation behaviour of chitosan bioelectret in aqueous solution using a fluorescence probe

A kind of intramolecular charge-transfer compound, 3-hydroxy-6-methyl-4′-N,N-dimethylamino flavone derivatives (PF), was used to detect the self-association of chitosan bioelectret in aqueous solution. Results showed that the fluorescence intensity of PF at 430 nm increased with increasing chitosan concentration in 0.1 M acetic acid, and concomitantly, the emission at 515 nm decreased. However, no emission was observed at 515 nm after the polarization of chitosan solution and only an increase in the peak of PF at 430 nm could be found. When 0.1 M hydrochloric acid was used to dissolve chitosan and all other conditions were the same as above, the PF peak was weak and did not disappear after the chitosan solution was polarized. In addition, the effect of ionic strength on chitosan aggregation with a concentration of 5 mg ml-1 before and after polarization was examined. The results also showed that the fluorescence intensity of the probe increased remarkably at 430 nm with increasing ionic strength after polarization of the chitosan solution. All the results indicated that polarization can promote the aggregation behaviour of chitosan in aqueous solution. © 1998 Chapman & Hall

Geminate recombination of long-lived electron-hole pairs in doped carbazole-containing amorphous molecular semiconductors

This paper reports an investigation into the features of geminate recombination of long-lived electron-hole pairs in films of poly(N-epoxypropylcarbazole) (PEPC) containing intramolecular charge transfer compounds as centers of photogeneration of charge carriers carried out by measuring the attenuation kinetics of isothermal recombination luminescence over a wide range of temperatures (4.2–300 K) for times t>1 s, along with the kinetics of photoinduced EPR signals. A study is made of how the presence of a potential barrier to the reverse transition of carriers to the recombination center and the initial triplet state of the charged pairs affects the geminate recombination. It is established that the kinetics of isothermal recombintation luminescence attenuation follow the law I(t)∝t −m for the times under study, where m takes values from 0.65 to 1.05. The first observations of a nonmonotonic change in m with temperature are reported (m passes through a minimum at a certain temperature), and a mechanism is proposed for recombination of charged pairs in PEPC containing intramolecular charge-transfer compounds as an explanation for this phenomenon.

Efficient up-conversion fluorescence in charge transfer compound crystal

A series of new intramolecular charge transfer compounds with absorption bands in shorter wavelengths have been synthesized. Bright visible light emits from the crystals of these new compounds under infrared pulsed laser pumping. The spectral and pump density dependent properties demonstrate that some of the emissions are up-conversion fluorescence due to two photon absorption. The fluorescent yields of one- and two-photon absorption are in the same order at high pump density. This work demonstrates that these new intramolecular charge transfer crystals are good candidates for nonlinear optical materials.

Fluorescence from the Twisted Intramolecular Charge Transfer Compound Bis(4,4′-dimethylaminophenyl)sulfone in Ethanol/CO2: A Probe of Local Solvent Composition

Fluorescence spectra and decays of bis(4,4′-dimethylaminophenyl)sulfone (DMAPS) in mixed ethanol/CO2 supercritical fluid solution have been examined in order to evaluate the local solvent polarity of the mixed fluid solvents. Solvatochromic shifts and band intensities have been determined by nonlinear regression analysis, and are compared with shifts and intensities observed in liquid n-alcohols. The spectral parameters of DMAPS in the mixed supercritical fluid solvents have been used to estimate enrichment of the local solvent composition in the polar modifier, under the assumption that the increase in solvent polarity over that calculated for the bulk fluid is the result of augmentation of the fluid composition in the region immediately surrounding the solute molecule. The analysis indicates that the local composition is enriched by a factor of five to ten over the bulk composition.

New advances in molecular engineering for quadratic nonlinear optics

Optimization of organic molecules for quadratic nonlinear optics is investigated in the perspective of nonlinearity/transparency trade-off, using intramolecular charge-transfer compounds with limited conjugation, such as oligomers of polysilane or polyphenyl. A large increase of the transparency in the blue and near UV spectral range is obtained for silane derivatives, but at the cost of a limitation of the nonlinear optical response at the molecular scale. On the contrary, polyphenyls appear to be ‘optimized’ materials, their nonlinear optical performances, both at the microscopic and macroscopic scale, being much better than those of paranitroanilines, with a significant improvement of the transparency. On the other hand, organometallic complexes containing ferrocene moieties conjugated to Ni, Pd or Pt metals through an organic polarizable unit display interesting nonlinear optical properties: the role of complexation appears to be quite important for ferrocenyl-containing ligands. A metal-to-metal intramolecular charge transfer is clearly evidenced. The role of the nature of the complexing metal and the influence of the nature of the ligand are also investigated. The moderate static hyperpolarizability values (of the order of 20 × 10 −30 e.s.u. may be partially accounted for by the defavourable projection factor between the ground state dipole moment and the vector part of the molecular hyperpolarizability.

The Spectra and Photophysics of the Intramolecular Charge Transfer Compound

The Spectra and Photophysics of the Intramolecular Charge Transfer Compound

Non-radiative deactivation of p-( N,N-dialkylamino)benzylidenemalononitriles

Intramolecular charge-transfer compounds of the p-( N,N-dialkylamino)-benzylidenemalononitrile series exhibit a weak fluorescence emission due to efficient non-radiative deactivation of the S 1,et excited state by a complex free rotor mechanism. In general, three possible channels are implicated in this deactivation; when all three channels are active, a synergistic effect is developed across the molecule. Examination of the non-radiative rate constant and apparent activation energy of reorientation in viscous medium (glycerol) for different compounds of the series provides an indication of the relative structural modification which occurs during the non-radiative deactivation via each channel.

Time-resolved fluorescence spectroscopy of a twisted intramolecular charge transfer compound bonded to polymers

Time-resolved fluorescence spectroscopy of a twisted intramolecular charge transfer compound bonded to polymers

INTRAMOLECULAR CHARGE TRANSFER TRANSITION FOR SYMMETRY ALLOWED CHARGE TRANSFER INTERACTION IN THE MOLECULES OF Cs SYMMETRY AND A POTENTIAL MODEL TO INTRODUCE NEW INTERSTACK INTERACTION

Abstract Three intramolecular charge transfer (CT) compounds, which exhibit clear CT transition for symmetry allowed CT interaction, have been synthesized and examined. In addition, a possible way to introduce new type of interstack interactions in the solid state was proposed from the crystal structure of 7,10-ethenocyclohepta-[de]naphthalene-8,9-dicarbonitrile.

High pressure study of luminescence from intramolecular CT compounds

The effects of high pressure on the luminescence properties of four organic intramolecular charge transfer compounds were investigated. The compounds were studied in a wide range of liquid and polymeric environments, and for one of the compounds, the effect of chemical substitution was also examined. In general, an increase of pressure affects the luminescence in a way which is in some degree similar to an increase of solvent polarity. A single configuration coordinate model was used to interpret the luminescence in terms of excited state interactions. Three of the compounds exhibited only fluorescence: p-(9-anthryl)-dimethylaniline (ADMA), 6-propionyl-2-dimethylaminonaphthalene (PRODAN), and 1-anilino-8-naphthalenesulfonate (ANS). Fluorescence from the first two compounds in nonpolar media is attributed to an excited state relatively unaffected by the charge transfer process. In polar media, fluorescence is believed to originate from another excited state that possesses considerable charge transfer character, and whose energy is strongly influenced by solvent polarity. At high pressure, an apparent fluorescence shift to higher energy was observed in viscous alcohols apparently due to the introduction of fluorescence from the energetically higher lying non-charge transfer excited state. This explanation is supported by the dual fluorescence decay observed from ADMA coincident with the sign reversal in fluorescence peak shift. Three excited states are believed to affect ANS fluorescence, two of them with charge transfer character. The model describing the excited states of ADMA and PRODAN is consistent with ANS fluorescence except in glycerol, whose anomalous behavior is discussed in the text. The fourth compound, nitroaniline, was studied in its three isomeric forms, with and without N-methylation. In addition to affecting the phosphorescence and fluorescence of p-nitroaniline, pressure studies indicate that nπ* singlet and triplet states figure prominently in the radiative and nonradiative processes of o-nitroaniline and m-nitroaniline as well.

The Electronic Spectra of Intramolecular Charge-transfer Compounds and Their Marked Solvatochromism in a Strong Hydrogen-bonding Solvent: 2-(Arylmethylene)-1,3-indandiones and 2-(1-Naphthyl)-p-benzoquinone

Abstract The first electronic absorption bands of the title compounds can all be assigned to the intramolecular charge-transfer transitions. The solvent effects on these bands are quite analogous to those on the absorption bands characteristic of binary charge-transfer complexes. Especially, when the title compounds are dissolved in trifluoroacetic acid, marked bathochromic shifts of the first bands are observed, in harmony with their charge-transfer character. Such solvatochromism is obviously due to the hydrogen-bond formation between the solute and the solvent molecules. When strong hydrogen bonding occurs, the electron affinity of the 2-methylene-1,3-indandione moiety increases by about 0.41 eV.