Donor–acceptor organogels and xerogels from C3-symmetric pyrene and naphthalene-diimide components

Abstract

Construction of gel- or xerogel-based materials by associating several components has increasingly attracted the attention of chemists over the last decade. It constitutes a valuable strategy to access gels with tailored properties, notably in the field of photo- and/or electroactive materials. In this context, we recently demonstrated that a C₃-symmetric gelator (C₃Pyr) endowed with three electron-rich pyrene units forms gels in the presence of electron poor additives. More than affecting the gelling behaviour, these derivatives strongly influenced the spectroscopic properties (absorption and emission) of the corresponding materials. This assessment prompted us to design a new C₃-symmetric derivative (C₃NDI) grafted with electron poor naphthalene diimide (NDI) units, to explore the well-established electronic complementarity with pyrene functional groups and promote the supramolecular co-polymerisation of C₃Pyr and C₃NDI into alternate stacks. Thereby, the corresponding bi-component organogels were characterized through a wide range of techniques, including NMR, UV-visible absorption and fluorescence spectroscopies, variable-concentration and variable-temperature measurements, and scanning electron and confocal microscopies. According to the solvent of preparation, remarkably different behaviours were observed, both gelators acting in either an antagonist or a synergetic manner. Since charge transfer interactions between pyrene and NDI units were set up along the gel formation, the formation and the dissociation of the aggregates could be probed through variable temperature measurements. The latter notably highlighted the extent to which the presence of a C₃-symmetric platform organising the NDI units contributes to the enhancement of the melting temperature. Finally, this study highlights how relevant modern confocal microscopy can be used to study such co-assembly.