The effect of intermolecular interaction on excited states in p-DTS(FBTTH2)2.

Using optical spectroscopy in solution and thin film, and supported by quantum chemical calculations, we investigated the aggregation process of the donor-acceptor type molecule p-DTS(FBTTH2)2. We demonstrate that cooling a solution induces a disorder-order phase transition that proceeds in three stages analogous to the steps observed in semi-rigid conjugated polymers. By analyzing the spectra, we are able to identify the spectral signature of monomer and aggregate in absorption and emission. From this we find that in films, the fraction of aggregates is near 100% which is in contrast to films made from semi-rigid conjugated polymers.