title: Solvent-Controlled Excited State Relaxation Path of 4-Acetyl-4'-(dimethylamino)biphenyl.
abstract: Stationary and picosecond time-resolved fluorescence (TRF) and absorption spectra were compared in different aprotic solvents at various temperatures for 4-acetyl-4'-(dimethylamino)biphenyl (ADAB). A large value of the excited state dipole moment, 18-25 D, was estimated from the plot of solvatochromic shift. TRF spectra of ADAB recorded as a function of solvent polarity and temperature show unusual temporal evolution (shift and decay) of the fluorescence bands. In some cases, the dynamic Stokes shifts occur on a time scale much shorter than expected on the basis of literature data on solvent relaxation. In order to investigate variations in the energy of electronic transitions, oscillator strengths, and dipole moments upon changing the molecular geometry, quantum chemical modeling (DFT, TD-DFT, CIS) was performed for ADAB and its ground-state pretwisted derivative, 4-acetyl-4'-dimethylamino-2,2'-dimethylbiphenyl (ADAB-Me). Combination of spectroscopic data and computational results leads to the model of excited state relaxation which involves dynamic solvent-dependent interaction between two close-lying (1)nπ* and (1)ππ* excited electronic states.
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warsaw, Poland.
authors.forename: J
authors.initials: J
authors.lastname: Dobkowski
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warsaw, Poland.
authors.forename: M
authors.initials: M
authors.lastname: Kijak
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warsaw, Poland.
authors.forename: I V
authors.initials: IV
authors.lastname: Sazanovich
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warsaw, Poland.
authors.forename: J
authors.initials: J
authors.lastname: Waluk