Optical dynamics of molecular aggregates

The subject of this thesis is the spectroscopy and dynamics of molecular aggregates in amorphous matrices. Aggregates of three different molecules were studied. The molecules are depicted in Fig. (1.1). Supersaturated solutions of these molecules show aggregate formation. Aggregation is a process similar to precipitation of a solution. The loss of entropy in such a precipitation process is compensated by the gain in enthalpy. Molecular aggregates in solutions thus represent a metastable thermodynamic state. The organisation of aggregates in solution can be fixed by rapid cooling or rapid solvent evaporation. The molecules were selected because of the dramatic changes occurring in the absorption spectra upon formation of aggregates. The aggregates show absorption bands that are shifted to lower energy by more than 1000 cm-l, with respect to the monomer transition. The dynamics of the optical excitations that are formed after absorption of a photon by these aggregates is the main topic of this thesis.