Donor-acceptor-promoted gelation of polyaromatic compounds

Low molecular mass organogels are nonconventional polymeric structures in which a minute amount of low molecular weight compound can reversibly gelify the whole solution without forming covalent bonds between the monomers. In this article, we demonstrate that certain electron acceptors (taking dinitrobenzoates as model compounds) that are incapable of gelifying the solvent on their own can assemble as much as a 15-16-fold larger amount of polyaromatic hydrocarbons (PAHs) and form two-component donor-acceptor organogels in different solvents. At the core of the long-range order stand donor-acceptor pairs. We assess our claims by detailed H-1 NMR, spectrophotometry, fluorescence, and time-resolved fluorescence methods. The thermodynamics of the gelation process is described on the basis of temperature dependent H-1 NMR studies. We believe that, in this case, H-1 NMR provides direct quantification of the dissolved concentrations of the different species and therefore provides a direct way to measure the enthalpy, entropy, and free energy associated with gel formation.