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

J. Dobkowski and I. Sazanovich Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warsaw, Poland

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Received: 26 10 2007;

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(CH3)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.

DOI: 10.12693/APhysPolA.112.S-127 PACS numbers: 33.50.-j, 61.66.Hq