Photophysics, electrochemistry and structure of a pyrazolino[60]fullerene dendrimer in solid molecular films

A novel pyrazolino[60]fullerene dendrimer is studied in solid molecular films. Orientated monolayers of this donor-acceptor system are formed by means of the Langmuir-Blodgett (LB) technique. The fullerodendrimer exhibits high collapse pressures but a tendency to aggregate at the air-water interface. Nonetheless, the subsequent LB deposition process shows a good transfer behaviour onto a variety of substrates. Concurrently, cast dropped films are prepared to compare particular properties respect to those of the LB films. Steady-state absorption spectra imply J-aggregation through solution-LB-cast films. The photoinduced outcomes suggest an enhanced charge transfer between donor-acceptor in thin films via intermolecular effects, although an energy transfer process may coexists. Therefore, square wave voltammetry (SWV) is applied to study the electronic behaviour of the C60-dyad. The results are qualitatively correlated with the photophysics. Further, reflection-absorption infrared spectroscopy (RAIRS) and atomic force microscopy (AFM) are applied to analyse the structure of the films, which is the main responsible of their properties. In this regard, it can be distinguished the preferential intermolecular arrangement in LB films with respect to cast film, and an aggregation growing with increasing number of transferred monolayers in case of LB films, but upholding homogeneity all along the surface's coating, contrary to the cast heterogeneousness.