Along the way from molecules to devices. The role of supramolecular interactions

Intermolecular interactions drive in molecular materials cooperative and collective behavior, and new properties and phenomena are expected in the material with no counterpart at the molecular level. These phenomena, driven by supramolecular interactions, largely extend the scope of potential applications of molecular materials. Here we present a model for interacting polar and polarizable molecules, which applies to clusters (crystals, aggregates, films, etc.) of D-pi-A chromophores for application in NLO and/or molecular electronics. The molecular polarity and hence all molecular properties are largely affected by supramolecular interactions, so that the same molecule behaves in qualitatively different ways in different environments. Important collective effects are recognized with sizeable deviations from the standard excitonic picture. Even more important, brand new phenomena appear in supramolecular structures. Specifically, in clusters with attractive interactions cooperative behavior shows up most dramatically with the appearance of discontinuous charge crossovers and of bistable behavior. In the proximity of the bistable regime, new collective excitations appear and the absorption of a single photon drives a concerted multielectron transfer occurring on several nearby molecules.