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1

Emission of Acridine and its Aggregates Isolated in the Neon Matrix

100%

Prochorow J., Kozankiewicz B., Dongo Gemi B. B., Morawski O.

Acta Physica Polonica A

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1998

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vol. 94

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issue 5-6

749-760

EN

The results of experimental studies of fluorescence and phosphorescence of acridine in the low-temperature inert neon matrix, at 7 K, are reported. It is found that the low-temperature inert matrix of neon affects the energy levels of acridine molecules very weakly even as compared with nonpolar (aprotic) and non-reactive solvent (e.g. hexane) and that there are different sites for acridine molecules in the neon matrix. However, the observed fluorescence spectra are strongly dependent on the excitation wavelength and besides the different (monomer) sites other emitting species are also contributing to the observed fluorescence emission of acridine in the neon matrix. Clear-cut evidence of the formation of singlet excimers of acridine in the neon matrix demonstrates itself as a very broad and structureless fluorescence spectrum with a relatively large shift from the origin of monomer (site) fluorescence which is characterized by a very distinct vibrational structure. The phosphorescence emission was observed only for the monomers. The observed differences in the low-energy part of excitation spectra of phosphorescence and fluorescence are discussed in terms of the close-lying excited singlet states of n,π* and π,π* character (mixed by the vibronic coupling) and tentatively interpreted as due to the formation of resonance acridine dimers. Their fluorescence spectrum is slightly shifted toward lower energies from the origin of monomer (site) fluorescence.

2

Ultrafast Energy Relaxation and Excitation Delocalization in Excited States of Zinc Porphyrin Dimers and Trimer

100%

Yamazaki I., Akimoto S., Yamazaki T., Shiratori H., Osuka A.

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vol. 95

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issue 1

105-120

EN

Ultrafast excited-state relaxation process has been studied with zinc porphyrin dimers and circular trimer. Following 80 fs excitation at Soret band (420 nm) or Q band (580 nm) of zinc porphyrin, the fluorescence decay curves exhibit ultrafast decays with lifetimes of 80 fs in o-dimer, 450 fs in trimer and 540 fs in m-dimer. The timeresolved fluorescence spectra show that the fast decay process correspond to disappearance of monomer-like emission followed by red-shifted and broaden spectra. These ultrafast processes are assigned as due to excitation transfer among monomers and delocalization of excitation yielding excitonic states.

3

Picosecond Transient Absorption of Xanthene Dyes

80%

Berndt O., Bandt F., Eichwurzel I., Stiel H.

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vol. 95

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issue 2

207-220

EN

After one- and two-colour ps-excitation the transient absorption of rose bengal, erythrosin B and eosin Y in the spectral range from 450 to 670 nm was probed using picosecond continuum pulses generated in H_{2}O-D_{2}O mixture. Our experiments showed for all dyes a high T_{1}-T_{n} absorption signal above 590 nm where no ground state absorption occurs. These excited triplet states can be effectively populated by a delayed second pump pulse. Their properties with special attention to reverse intersystem crossing processes from T_{n} to S_{x} are discussed.

4

Excited States in Solid Phenothiazine as Studied by Electroabsorption Spectroscopy

80%

Kalinowski J., Stampor W., Fattori V., Di Marco P.

Acta Physica Polonica A

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1995

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vol. 87

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issue 6

953-964

EN

Electric field modulated absorption spectra of vapor deposited layers of phenothiazine, explained in terms of a quadratic Stark effect, indicate modification of intramolecular (Frenkel-type) excitons by charge transfer transitions throughout UVIS absorption spectrum in the range 250-450 nm. The charge transfer character of the excited states appears at energies characteristic of various oxidation products of phenothiazine as identified from a spectroscopic study of photochemical air oxidation, performed on solution and solid film samples of this compound. The charge transfer transitions are ascribed to electron transfer between the molecules of phenothiazine and their oxidized species created in the samples during preparation and handling procedures.

5

Luminescent Probe for Highly Energetic Collisions in Mixtures of Complex Molecules with Acceptors of Vibrational and Triplet Energy

80%

Zalesskaya G., Yakovlev D., Sambor E., Baranovsky D.

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vol. 95

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issue 6

897-910

EN

Pressure dependences of intensities and decay rates of time-resolved luminescence of acetophenone, benzophenone, anthraquinone were used to obtain the efficiencies of vibrational and triplet-triplet energy transfer. It was shown that vibrational relaxation of the chosen molecules can be interpreted in terms of two consecutive processes: rapid collisional relaxation of molecules from initially prepared states to a vibrational distribution at T_{vib} by vibration-vibration process and relaxation of this vibrational distribution to the thermal one (vibration-translation process). At relatively small internal energy < 10000 cm^{-1}, the collisional efficiencies of the vibration-vibration process in mixtures with polyatomic bath gases had values typical of processes with a supercollision contribution. Molecules relaxed from the upper vibrational level to the vibrational distribution after several collisions (2-3). The average energies transferred per collision are well correlated with predictions of the simple ergodic theory of collisional energy transfer. The majority of the collisions took part only in vibration-translation energy transfer of relatively small energies. The efficiencies of triplet-triplet energy transfer were analyzed for acetophenone, benzophenone and anthraquinone as donors and biacetyl-acceptor in a gas phase when energy of about 20000 cm^{-1} was transferred. It permitted us to elucidate the common features of highly energetic collisions. It was shown that the efficiencies are much lower than the gas kinetic ones and depended on the vibrational energy and temperature. It was discussed how to enhance triplet-triplet efficiencies due to vibrational excitation of a donor molecule.

6

Spectroscopy of 2-aminopurine: An MCSCF Study

80%

Rachofsky E., Ross J., Krauss M., Osman R.

Acta Physica Polonica A

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1998

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vol. 94

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issue 5-6

735-748

EN

2-aminopurine is a highly fluorescent isomer of adenine that can be incorporated into DNA as a probe of structure, dynamics, and protein-DNA interactions. Interpretation of the fluorescence of 2-aminopurine in DNA requires a model of the electronic structure of this fluorophore in its ground and excited states. To this end, electronic structures and energies of the ground and lowest singlet excited states of 2-amino-9-methylpurine were calculated by the multiconfiguration self-consistent field method supplemented by multiconfiguration perturbation theory. The molecular geometry was optimized in both of these electronic states to permit investigation of both electronic excitation and fluorescence emission. The predicted energies and transition dipoles were in good agreement with experiment. The permanent molecular dipole of 2-amino-9-methylpurine increased upon excitation, suggesting that both the absorption and emission spectra should shift to slightly lower energies in polar solvents. The anomalous spectral shifts observed in water suggest that 2-aminopurine undergoes hydrogen bonding that better stabilizes the ground state than the excited state. From the calculated electrostatic potentials of these two states, the position at which this hydrogen bond forms was predicted. These results form a basis for understanding the excited states and possible intermolecular interactions of 2-aminopurine in DNA.

7

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.

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Emission of Acridine and its Aggregates Isolated in the Neon Matrix

Ultrafast Energy Relaxation and Excitation Delocalization in Excited States of Zinc Porphyrin Dimers and Trimer

Picosecond Transient Absorption of Xanthene Dyes

Excited States in Solid Phenothiazine as Studied by Electroabsorption Spectroscopy

Luminescent Probe for Highly Energetic Collisions in Mixtures of Complex Molecules with Acceptors of Vibrational and Triplet Energy

Spectroscopy of 2-aminopurine: An MCSCF Study

Photoinduced Electron Transfer in Jet Cooled Molecular Complexes