Vibronic absorption spectra of molecular aggregates consisting of up to N = 9 monomer units are calculated employing methods of time-dependent quantum mechanics. Taking one vibrational degree of freedom for each monomer into account and treating one-exciton excited electronic states leads to a problem with N vibrations and N electronically coupled states. The demanding quantum propagation is carried out within the multiconfiguration time-depended Hartree method (MCTDH). Spectral features of and population transfer in the aggregates are analyzed as a function of the aggregate size and the strength of the electronic coupling. With a model for oligomers of perylene bisimides, it is shown how measured temperature-dependent absorption spectra correlate with the aggregate size. Furthermore, the exciton localization and dynamics in these aggregates are investigated.

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Swnmary Solvent magnetic anisotropy shifts for nonpolar solutes in benzene show a systematic decrease with increasing size of the solute molecule, in agreement with theoretical predictions based on a geometrical model.THE effects of solvents with magnetically anisotropic molecules (e.g. benzene) on n.m.r. chemical shifts are an aid to structure determination.1-* The resonance positions in the anisotropic solvent are compared with those for the same solute in an isotropic solvent (e.g. carbon tetrachloride), with an internal tetramethylsilane (TMS) reference in both solutions. For non-polar solutes, the collision complex model1 successfully applied to solutes with polar groups is inappropriate, and the shifts depend mainly on the size and shape of the solute molecules.