so that a direct comparison with the profile of the absorption spectrum becomes feasible. The normal modes were calculated on the 6-31G/MP2 level and the coupling to the optical transition on the CI/SD level. Using these couplings and the displaced harmonic oscillator model the lineshape was calculated as the Fourier transformed time correlation function. In the low frequency region the largest vibronic couplings are found for normal modes at 40 and 46 cm − 1 which contribute significantly to the broadening of the absorption band. Another important contribution from modes around 1500 cm − 1 which are also known from Raman spectra is the origin of the observed vibrational progression. Further modes between 50 and 1400 cm − 1 form a rather dense continuum of coupling states. The simulated spectrum (fig. 2) largely resembles the experimental absorption profile. The width of the simulated bands is somewhat too small and the intensity of the prominent stretching modes is slightly overestimated. This could be possibly further improved by taking frequency changes and mode coupling into account. The MD simulations were started from several plausible dimer structures. First the PIC molecules were kept fixed and the solvent was equilibrated for 50 psec. Then the restraints were removed and the system was simulated for another 50 psec. The distance and orientation of the two PIC molecules were analyzed to identify periods of relative stability. Starting from a sandwich structure, a rather stable structure evolved within 10 psec (fig.3a). It is not symmetric but still there is almost no splitting of the calculated site energies (Table 2) which show rapid fluctuations with components down to 20fsec. Such fast fluctations are well known from experimental and theoretical work on the dynamics of dephasing and solvation in molecular liquids 19 . They have been attributed to the inertial motion of the solvent molecules, which show up as the Gaussian shaped rapid initial decay of the solvation time correlation function 20,21 . In our simulations the orientational time correlation function of the water molecules can be described by a Gaussian with a correlation time of 60 fs at short times. The time correlation of the electrostatic potential decays faster. The initial Gaussian decay with 20 fs is very similar to that of the correlation function of the transition energies. Probably collective librational motions contribute more efficiently to the electronic dephasing than the motion of the individual molecules. 19,22 The center of the site energies is shifted by 0.06 eV to lower energies as compared to a monomer in vacuum and the variance of the site energies is comparable to that of a monomer. The two transition dipoles are almost parallel and the lower transition carries 5