Donor-Acceptor Crystalline Supramolecular Polymers (DACS) for Solar Energy Harvesting Applications

摘要

The conversion of light into chemical energy, the programmed movement and rearrangement of cells, or the storage and translation of genetic information in nature occur because of the critical role of stimuli-responsive, structurally dynamic biopolymers that possess reversible noncovalent binding groups capable of both inter- and intrachain interactions. Supramolecular polymers that assemble from monomers into polymers as a result of noncovalent, rather than covalent, bonding have been increasingly explored for a variety of materials, but their utility in energy harvesting remains unproven. To create a new class of materials for energy harvesting applications where the molecular structure is controlled precisely in 3D as a result of well-understood self-assembly processes, a series of electron donors and electron acceptors that form supramolecular polymers upon mixing in solution have been developed. The acceptors are based on the perylene diimide (PDI) scaffolds and the donors are comprised of diketopyrrolopyrroles (DPPs) modified with terminal diamidopyridines that form complementary Hydrogen bonds (H-bonds) with the PDIs. Upon assembly, supramolecular polymers are formed that precipitate into thin films that are organized by noncovalent interactions including H-bonding, pi-pi stacking, and hydrophilic-hydrophobic contacts. The assembly of these materials in solution was studied by variable temperature (VT) 1H NMR spectroscopy, and the peak shifts indicative of H-bonding were fitted to a polymeric binding model to determine quantitatively the thermodynamic parameters of binding (ΔH~o, ΔS~o) and to confirm their temperature and concentration dependent formation into linear oligomers and polymers. Electronic and assembly properties of these materials are strongly dependent on the donor and acceptor structures, and subtle changes to the molecular structure of either have drastic consequences on binding strength and subsequent assembly.