We are investigating the excited-state dynamics of a triad synthesised in the group of Prof. Matile at the University of Geneva. It consists of a central naphthalene diimide (NDI) unit attached to two core-substituted NDIs (rNDI). Upon optical excitation of a rNDI unit, the fluorescence dynamics of the triad in acetonitrile (blue trace) is biphasic with picosecond and nanosecond decay components (blue trace). As shown by transient absorption measurements, this decay is due to the occurrence of a charge separation between the excited rNDI (electron donor) and the central NDI units. The biphasic nature of the dynamics arises from the presence of several conformations in liquid solution. The fluorescence decay of the same triads organised on an ITO surface is much faster (red trace) because of the occurrence of additional charge separation pathways.
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