Photophysical characterization of low-molecular weight organogels for energy transfer and light harvesting

The choice of a donor and an acceptor with suitable optical and self-assembly properties is essential in the design of organogel-based light harvesting systems. Organogels can provide supramolecular structures capable of enhancing energy transfer processes. In this work, we present the characterization of N-(naphthalene-1-carboxyamide)-(3S,4S)-pyrrolidin-(3,4)-bisdodecyl-carbamoyldiester (1) and N-(4-nitrobenzofurazan-7-amino)-(3S,4S)-pyrrolidin-(3,4)-bisdodecyl-carbamoyldiester (2) which are used as donor and acceptor moieties, respectively. The donor molecule is hardly capable to form a gelon its own but it can be assembled at reasonable concentrations with the acceptor gelator to form a two-component donor–acceptor organogels in cyclohexane. Stable organogels are formed from cyclohexane for gelator concentrations as low as ≈10−3 M. UV–vis and steady-state fluorescence spectroscopies were used to provide a characterization of their molecular interactions. The optical changes observed during the cooling of two-component solutions of these systems are indicative of typical sol–gel transitions. The occurrence of excitation energy transfer processes in the gels is confirmed by comparison of their excitation and absorption spectra.