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The Geometry of the Excited Charge Transfer States: Flattening or Twisting?

100%
Dobkowski J., Sazanovich I.
Acta Physica Polonica A
|
2007
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vol. 112
|
issue S
S-127-S-142
EN
Numerous molecules built of an electron acceptor and electron donor units linked together by single bond exhibit a peculiar behavior in their low-lying electronically excited states. N,N-diethylaminoacetophenone and 4-acetyl-4'-dimethylamino-biphenyl, having acetophenone as the acceptor and differentiated by the donors groups N(CH_3)_2 and dimethylaniline, respectively, were selected as the subject of study. To recognize the excited state relaxation paths the stationary and time-resolved spectroscopy in absorption and emission was applied. Experimental results indicate that after excitation in polar solvents N,N-diethylaminoacetophenone reduces to minimum the overlap between π-electron systems of the donor and acceptor groups relaxing to the twisted internal charge-transfer state; contrary to that, flattening of the 4-acetyl-4'-dimethylamino-biphenyl skeleton generates increase in the overlap of the π-electron systems.
2
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Picosecond Transient Absorption Spectra and the Twisted Intramolecular Charge Transfer Phenomenon

81%
Dobkowski J., Grabowski Z. R., Jasny J., Zieliński Z.
Acta Physica Polonica A
|
1995
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vol. 88
|
issue 3
455-468
EN
An improved model of a computer-controlled picosecond absorption spectrometer was designed and constructed. Its operation is described, and applied to the measurement of transient spectra of p-N, N-dioctylamino-acetophenone. The spectroscopy and photophysics of this compound are compared to the other compounds exhibiting the dual fluorescence, assigned usually to the adiabatic formation of the "twisted" intramolecular charge transfer excited state. The data are discussed in relation to alternative suggestion of an inversion of the pyramidal amino nitrogen atom. The whole evidence supports the decoupling of the π-electronic systems of D+ and A- in the D+-A- polar excited state, in full accord with the "twisted" intramolecular charge transfer model. The peculiar behaviour of the long alkyl -NR2 derivatives (favouring the "twisted" intramolecular charge transfer state emission) seems to be primarily due to the decreasing oxidation potential of such electron donor groups.
3
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Spectroscopy and Photophysics of 3'-[p-(dimethylamino)phenyl]spiro-[fluorene-9,4'-oxazolidine]-2',5'-dione

81%
Dobkowski J., Kołos R., Waluk J.
Acta Physica Polonica A
|
1995
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vol. 88
|
issue 3
445-454
EN
Electronic absorption and emission spectroscopy of the title molecule has been studied in solution, low-temperature glasses and polymer matrices. No luminescence could be observed down to 77 K. In the presence of water, the formation of the hydrated species was observed, accompanied by the appearance of phosphorescence. The structure and spectra of both forms were calculated using molecular mechanics and quantum chemical methods. The lack of phosphorescence in the anhydride is interpreted as due to proximity effects in the triplet manifold.
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