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1

Intramolecular Charge Transfer with N,N-Dialkyl-4-(Trifluoromethyl)anilines and 4-(Dimethylamino)benzonitrile in Polar Solvents. Investigation of the Excitation Wavelength Dependence of the Reaction Pathway

100%

Galievsky V., Zachariasse K.

Acta Physica Polonica A

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2007

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vol. 112

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issue S

S-39-S-56

EN

In the series of N,N-di-n-alkyl-4-(trifluoromethyl)anilines (DXCF3), with X = M (methyl), E (ethyl), Pr (n-propyl) and Pe (n-pentyl), an intramolecular charge transfer (ICT) reaction takes place in the polar solvent acetonitrile (MeCN). Such a reaction does not occur in the less polar solvents $n$-hexane and diethyl ether, in which a single fluorescence band from the locally excited (LE) state is observed. For DMCF3 in MeCN at 25ºC, the intramolecular charge transfer reaction efficiency is much smaller than for 4-(dimethylamino)benzonitrile (DMABN) in this solvent, as seen from the ICT/LE fluorescence quantum yield ratio Φ'(ICT)/Φ(LE): 0.06 for DMCF3 and 39.5 for DMABN. As predicted by the planar ICT (PICT) model, this difference is caused by the considerably larger energy gap Δ E(S_1,S_2) of DMCF3 (5750 cm^{-1}) as compared with that of DMABN (3130 cm^{-1}). When the alkyl chain length of DXCF3 becomes larger, Φ'(ICT)/Φ(LE) in MeCN at 25ºC increases, from 0.06 for DMCF3 to 0.64 for DPeCF3. This increase in ICT reaction efficiency is accompanied by a small but significant decrease of 380 cm^{-1} for Δ E(S_1,S_2) when going from DMCF3 to DPeCF3. Because of their relatively large Δ E(S_1,S_2) gap, the molecules DXCF3 are suitable for an investigation of the excitation wavelength dependence of the intramolecular charge transfer reaction. For DPrCF3 in MeCN, the same Φ'(ICT)/Φ(LE) is found for excitation in the S_1 or in the S_2 manifold. A similar result is obtained with DMABN in tetrahydrofuran. From these experiments it is concluded that for DPrCF3 and DMABN the intramolecular charge transfer reaction follows an adiabatic pathway. After excitation to a Franck-Condon S_n(FC) state, the electron donor/acceptor molecules first undergo ultrafast internal conversion to the relaxed LE(S_1) state, from which precursor the reaction proceeds to the ICT state. Experimental evidence for a nonadiabatic ICT reaction pathway, going directly from S_2(FC) via an S_2/S_1 conical intersection to the LE and ICT state, is not found. This pathway would lead to an enhancement of the ICT population, i.e., to an increase in Φ'(ICT)/Φ(LE), as compared with the adiabatic LE → ICT reaction.

2

Electronic Spectra of Radical Cations and their Correlation with Photoelectron Spectra. VI. A Reinvestigation of Two-, Three-, and Four-Ring Condensed Aromatics

80%

Khan Z.

Acta Physica Polonica A

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1992

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vol. 82

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issue 6

937-955

EN

Earlier interpretations of the electronic spectra of two-, three-, and four-ring condensed aromatic hydrocarbon radical cations are reexamined in the light of the UV photoelectron spectroscopic data for their neutral precursors and improved open-shell self-consistent field configuration interaction (SCF-CI) calculations. From the electronic transition energies for some 33 aromatic radical cations obtained from electronic absorption spectra (EAS) and those inferred from photoelectron spectra (PES), the following correlation is found between the two types of spectroscopies: E_{EAS} = (0.23 ± 0.20) + (0.98 ± 0.01)E_{PES}. The slope of this line is very close to unity which shows that the matrix shift on going from the solid phase (electronic spectrum) to the vapour phase (PE spectrum) is almost negligible and that there is no appreciable change in the geometry of the molecules on ionization.

3

Molecular Interactions in Monolayers οf Azo Dye/Liquid Crystal Mixtures at Interfaces

80%

Bauman D., Płóciennik A., Inglot K.

Acta Physica Polonica A

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2009

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vol. 116

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issue 2

203-210

EN

A study of azo dye/liquid crystal mixtures in monolayers formed at an air-water interface (the Langmuir films) and at a solid surface (the Langmuir-Blodgett films) has been performed. Five azo dyes with various molecular structure and the liquid crystal 4-octyl-4'-cyanobiphenyl (8CB) have been used. The dyes have been added to the liquid crystal at various molar fractions. Surface pressure and surface potential versus mean molecular area isotherms for the Langmuir films have been recorded and information about intermolecular interactions at the air-water interface has been obtained. On the basis of electronic absorption measurements for the Langmuir and Langmuir-Blodgett films the conclusions about the ability of dyes molecules to form self-aggregates at the interfaces have been drawn. The influence of the dye molecular structure and its concentration on aggregates' geometry has been found.

4

Diagnostics of a Hydrocarbon Plasma Jet Using the A^{2}Δ-X^{2}Π System of CH

80%

Koulidiati J., Czernichowski A., Beulens J., Schram D.

Acta Physica Polonica A

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1998

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vol. 94

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issue 1

3-12

EN

We study the intensity distribution of the A^{2}Δ-X^{2}Π system of CH molecule at 430 nm in a low pressure plasma jet. This system shows an overlap of vibrational bands with Δv=0. By comparing simulated and experimental emission spectra, we obtain rotational and vibrational temperatures using Boltzmann plots or some thermometer functions. The thermometer functions are the integrated intensities of line-like transitions composed of several rotational transitions. The result of the Boltzmann plots and the thermometer functions method that we propose are in good agreement.

5

Mesure de la Temperature Basees sur l'Observation du Premier Systéme Negatif de l'Azote

80%

Nassar H., Czernichowski A.

Acta Physica Polonica A

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1993

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vol. 84

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issue 2

215-228

EN

Noisy, non-resolved emission spectra of the (0,0) 391.4 nm N_{2}^{+} molecular band are employed for the rotational (and in some case vibrational) temperature evaluation in different sources in the range of 320-7900 K when the apparatus function of the recording system is unknown. The following sources are examined: an ovoid-shaped transferred arc at atmospheric pressure, a low-pressure transferred arc, a high-voltage high-pressure electric discharge, a low-pressure radio-frequency discharge, and an atmospheric pressure laminar plasma jet. The described method is based on a normalization of the experimental spectrum with respect to the (0,0) band-head amplitude followed by a point-to-point comparison of the real spectrum with respect to a computer simulated spectrum using the best-square fit criterion. This criterion is found as the good one: the relative error on temperature evaluation had the same order of magnitude as the noise-to-signal ratio, even if the last one was relatively high. It was also found that the rotational and vibrational temperatures in the radio-frequency discharge are very different, which indicates an out of thermodynamic equilibrium characteristic of such a discharge. The proposed method of temperature evaluation is shown as quite precise and simple to use for even the non-spectroscopists.

6

Light-Induced Tautomerization in Porphyrin Isomers

80%

Waluk J.

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vol. 95

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issue 1

49-62

EN

Double proton tautomerization occurring in porphyrin and its structural isomers represents a special case of a chemical transformation in which the substrate and the product are form ally the same. The methods used for the investigation of this kind of processes are based on polarized spectroscopy and high-resolution techniques, such as matrix isolation. Their combined use results in obtaining information pertinent to the mechanism of proton transfer, regarding e.g., the values of proton transfer rates, structure of the tautomeric forms or the shape of the potential energy surfaces. In addition, these procedures provide a way of obtaining spectral, photophysical and structural data that would be otherwise difficult to gain. The examples include determination of transition moment directions, assignment of electronic and vibrational states, elucidation of the character of the substitutional replacement of the rare gas matrix atoms by the chromophore, and the analysis of the nature of the symmetry lowering due to the matrix cage.

7

Deformation of a Spherical Molecule

80%

Apostol M.

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EN

The deformation suffered by a hollow, spherical molecule as an effect of rotations is studied within a continuum model which might be relevant for the fullerene molecule. The spherical elasticity is established to the lowest order in deformations and the natural perturbation parameter required by the stability of the object is identified as the square ratio of the rotation to the radial vibration pulsations. It is also shown that the main effect of the centrifugal coupling between rotations and radial vibrations is a static deformation whose energy is beyond the harmonic approximation.

8

Electronic States and Structure of Dibenzo[j,lm]-phenanthro[5,4,3-abcd]perylene

80%

Marczyk J., Waluk J., Fetzer J.

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EN

Electronic absorption and emission, fluorescence anisotropy and linear dichroism techniques were applied to dibenzo[j, lm]phenanthro[5,4,3-abcd]perylene in order to determine its electronic structure and check the possibility of existence of conformational isomers. The results indicate the presence of only one conformer. Its structure is proposed on the basis of the experimental data as well as molecular mechanics and quantum chemical calculations.

9

Influence of Silver Colloid on Fluorescein Spectral Properties

80%

Frąckowiak D., Balter A., Karolczak J., Siejak P.

Acta Physica Polonica A

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2006

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vol. 110

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issue 4

451-458

EN

In order to check if the observed earlier changes in fluorescence intensities of fluorescein solution due to the addition of colloidal suspension of silver are related to the generation of surface plasmon coupled emission, the steady state photothermal spectra and fluorescence decay times of such samples were measured. The Gaussian components of photoacoustic spectra for solutions with and without silver colloid addition were determined and compared with components of absorption and fluorescence excitation spectra of the same samples. The efficiencies of thermal and radiative deactivation of various samples were discussed. The fluorescence decay times measured at the wavelength of excitation not exhibiting the increase in photonic mode density depend only on the dye concentration. Decays exhibit changes as a result of silver addition with excitation in the region in which enhancement of fluorescence is observed. These changes are due not only to the change in the fluorescence yield generated by interactions with plasmons but also to those in thermal deactivation of the sample related to the colloid presence.

10

Solvatochromic Effect in a Benzimidazole-Based Betaine: Determination of the Dipole Moments and Second-Order Hyperpolarizability

80%

Ziółek L., Palewska K., Lipiński J., Sworakowski J., Nes̆půrek S., Böhm S., Meister E. C.

Acta Physica Polonica A

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1995

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vol. 88

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issue 2

283-293

EN

Results of measurements of the solvent-dependent shift of the low-energy absorption band solvatochromic effect in a benzimidazole-based betaine are reported in the paper. Measurements of absorption spectra in several solvents of different polarities were performed. The solvatochromic shift of the low-lying absorption band was found to exceed 3000 cm^{-1}; the results obtained were then employed to calculate the ground- and excited-state dipole moment of the molecule. The spectroscopic measurements were supplemented by measurements of the ground-state dipole moment. A remarkable change in the charge distribution was found to occur upon the electronic excitation: both the experimental results and the calculations indicate that the ground-state dipole moment is close to 13 D, whereas in the excited state it amounts to ca. 3 D. The second-order hyperpolarizability of the molecule was calculated from the measurements; its off-resonance value amounts to ca. 20 × 10^{-40} m^{4}/V (4.8 × 10^{-30} esu), depending on the solvent used.

11

Photoinduced Electron Transfer in Jet Cooled Molecular Complexes

80%

Piuzzi F., Uridat D., Dimicoli I., Mons M., Tramer A., LeBarbu K., Lahmani F., Zehnacker-Rentien A.

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vol. 95

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issue 1

121-135

EN

Exciplex and excimer formation have been probed in several jet cooled complexes using mass selective two-photon ionisation and fluorescence excitation spectroscopy as well as ground state depletion spectroscopy (hole burning): (i) In the anthracene-dimethyl-ortho-toluidine system, it has been found that the ionisation step takes place with a much higher efficiency from the charge transfer state responsible for the exciplex emission than from the locally excited state giving rise to the resonant fluorescence. (ii) The dimer, trimer, and higher clusters of anthracene all show only excimer emission. When compared to the dimer, the trimer exhibits a peculiar behaviour (structured fluorescence excitation and hole burning spectra, short lifetime and low ionisation efficiency) which has been related to a significant locally excited character of the initially prepared state of the species excited state. (iii) The influence of an intermolecular hydrogen bond on the electron transfer process has been studied in the 2,2,2-trifluoro-1-(9-anthryl)ethanol- dimethylaniline system. A threshold for exciplex formation higher than in the case of the anthracene-dimethylaniline complex is observed.

12

1,1'-Dithiolenes: the Good, the Not Bad, and the Ugly

70%

Cassoux P., Bowlas C. J., Lahlil K., Moradpour A., Bonvoisin J., Launay J.-P.

Acta Physica Polonica A

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1995

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vol. 87

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issue 4-5

743-748

EN

A series of 1, 1'-dithiolate ligands were used in the attempted preparation of metal complexes. These bidentate sulphur ligands were subsequently used in aromatic nucleophilic substitution reactions giving rise to several novel organic donor molecules. The electrochemistry data of two of the donors and their subsequent use in the preparation of donor-acceptor compounds is presented. One donor-acceptor compound exhibited high room temperature conductivity (up to 900 S cm^{-1}) and remained metallic down to low temperature. One donor containing two tetrathiafulvalene units was studied by near infrared absorption spectroscopy. An intervalence transition in the monocation form of this donor was observed, indicating that it behaves as a class II mixed valence compound.

13

Spectral Investigations of Fullerene-Porphyrin Complexes

51%

Barszcz B., Bogucki A., Laskowska B., Ion R., Graja A.

Acta Physica Polonica A

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2007

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vol. 112

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issue S

S-143-S-152

EN

Spectral investigations of someμ-oxo-dimer complexes of trivalent metals (Mn, Fe) with two different ligands: tetraphenylporphyrin and tetranaphthylporphyrin (TNP), and fullerene (C_{60} and C_{70}) complexes withμ-oxobis[5,10,15,20-tetraarylporphyrinatometal (III)] (TXP-M)_2O dimer, where M = Fe, Mn and X = phenyl or naphthyl, are presented. Discussion of the main electronic and vibrational bands observed in the UV-Vis-IR and Raman spectra of both classes of fullerene-porphyrin systems is given. Experimental data are completed with the quantum chemical calculations of MnTNP^+ component.

Refine search results

Intramolecular Charge Transfer with N,N-Dialkyl-4-(Trifluoromethyl)anilines and 4-(Dimethylamino)benzonitrile in Polar Solvents. Investigation of the Excitation Wavelength Dependence of the Reaction Pathway

Electronic Spectra of Radical Cations and their Correlation with Photoelectron Spectra. VI. A Reinvestigation of Two-, Three-, and Four-Ring Condensed Aromatics

Molecular Interactions in Monolayers οf Azo Dye/Liquid Crystal Mixtures at Interfaces

Diagnostics of a Hydrocarbon Plasma Jet Using the A^{2}Δ-X^{2}Π System of CH

Mesure de la Temperature Basees sur l'Observation du Premier Systéme Negatif de l'Azote

Light-Induced Tautomerization in Porphyrin Isomers

Deformation of a Spherical Molecule

Electronic States and Structure of Dibenzo[j,lm]-phenanthro[5,4,3-abcd]perylene

Influence of Silver Colloid on Fluorescein Spectral Properties

Solvatochromic Effect in a Benzimidazole-Based Betaine: Determination of the Dipole Moments and Second-Order Hyperpolarizability

Photoinduced Electron Transfer in Jet Cooled Molecular Complexes

1,1'-Dithiolenes: the Good, the Not Bad, and the Ugly

Spectral Investigations of Fullerene-Porphyrin Complexes