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Time-Resolved Infrared Spectroscopy of Water. Relation between the OH Stretching Frequency and the OO Distance

Bratos S., Leicknam J. -C., Pommeret S.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 5

737-745

EN

It is shown how infrared pump-probe spectroscopy can be used to measure subpico second variations of the oxygen-oxygen distribution function in liquid water. A diluted solution HDO/D2O rather than pure H2O is considered to switch off resonant vibrational interactions between water molecules; the local structure remains unchanged in this substitution. The present study is limited to times superior to 100–200 fs. This permits to avoid problems generated by hard sphere type collisions between water mole ules, as well as the interference between ultrafast pump and probe pulses. It is then shown that the Novak-Mikenda type relations between the OH stretching frequency and the OO distance largely sur vive when going from standard to ultrafast infrared spectroscopy. More over, the infrared pump-probe profiles of OH stretching bands closely parallel the oxygen-oxygen distribution functions in this time do main. Infrared pump-probe spectroscopy is thus a use ful substitute of time-resolved X-ray diffraction in this exceptional case.

2

The Excited State Relaxation Path of N,N-Diethyl-5-cyanopyridine and N,N-Diethylbenzaldehyde

Dobkowski J., Sazanovich I.

Polish Journal of Chemistry

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2008

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Vol. 82, nr 4

831-845

EN

The molecules which possess, as electron donors, dialkylamino groups linked by a single bond with the acceptor subunits undergo fast excited state intramolecular charge transfer (ICT), emitting dual fluorescence in polar solvents. The short and the long-wave length fluorescence bands are traditionally assigned as Fb and Fa, respectively. The nature of the excited state from which the Fa emission originates, as well as the mechanism of energy degradation have been the subject of many controversies. As the objects of this study, 2-(N,N-di ethyl)-5-cyanopyridine (PEC) and p-N,N-diethylaminoacetophenone (DEABA) were selected. For these molecules different sequence of the two low-lying pi pi* La and Lb states was postulated, which can help to verify the excited state mechanisms of the charge separation. The experimental results obtained by stationary and time-resolved spectroscopy show that the anomalous Fa emission originates from the ICT state generated by the mutual twist of the donor and acceptor group (TICT model).

3

Time -Resolved Emission Spectroscopy of Pyrene Derivatives

Dobkowski J., Galievsky V., Jasny J., Sazanovich I.

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 7

961-972

EN

An improved model of the picosecond time-resolved spectrofluorimeter equipped with an optical Kerr shutter was designed and constructed. The instrument was applied for measurements of time-resolved fluorescence (TRF) spectra of 4_-(pyrenyl-1-yl)acetophenone (Py-BK) and 4_-(pyrenyl-1-yl)benzonitrile (Py-BN). The experimental results indicate that both molecules relax after excitation by mutual twisting of two subunits towards a more planar geometry. In the case of Py-BK the kinetics of creation of excited state hydrogen-bonded complexes was discussed in detail.

4

Time-resolved optical spectroscopy and imaging of breast

Taroni P., Pifferi A., Torricelli A., Cubeddu R.

Opto-Electronics Review

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2004

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Vol. 12, No. 2

249-253

EN

A fully automated system for time-resolved reflectance and transmittance spectroscopy from 610 to 1010 nm was developed and applied to the optical (absorption and scattering) characterization of breast tissue in vivo. From absorption spectra, information is derived on tissue content of oxy-, deoxyhemoglobin, water and lipids, while scattering spectra provide knowledge on tissue structure. A portable system for breast imaging at four wavelengths (683, 785, 912, and 975 nm) was also developed and is being tested in clinics for the detection and characterization of breast lesions (optical mammography).