Synthesis, structure and function of π-stacked polymers

Abstract

Macromolecular conformation often has a significant effect on the properties of polymeric materials, and hence, conformational control in synthesizing a polymer is an important goal in polymer science. As a new conformational motif of vinyl polymers having side-chain p-electronic groups, we have introduced a 'p-stacked structure' in which side-chain chromophores are regularly stacked on top of each other and main-chain C-C bonds have a nearly all-trans, zigzag conformation. p-Stacked polymers can be prepared by vinyl polymerization of dibenzofulvene (DBF) and its derivatives. On the basis of the controlled structure, poly(DBF) and its derivatives exhibit unique photophysical and electronic properties as vinyl polymers. In addition, introduction of chirality to p-stacked polymers was also achieved. In this review, the synthesis of poly(DBF) and its derivatives and their structural analyses and properties are described. Polymer Journal (2010) 42, 103-123; doi:10.1038/pj.2009 Keywords: charge transport; chirality; dibenzofulvene; helix; photophysical properties; p-stacked structureIn designing functional organic materials with desired properties, spatial arrangement control of constituent molecules is an important factor because molecules in a regulated assembly often indicate properties different from those in solution or in gas phase because of specific intermolecular interactions. Effective molecular assembly control can be achieved by arrangement of functional molecules as a part of a polymer chain with a regulated conformation and configuration in which the polymer backbone functions as a structural template or scaffold. This is possible either by polymerizing functional molecules as monomers or by attaching functional molecules through a chemical reaction to a polymer chain. In the former case, the functional molecules to be aligned need to have a polymerizable moiety such as a vinyl group; they are a part of monomers and become constituents of a polymer chain as a part of monomeric units, typically as side-chain groups. The monomer structure itself may significantly contribute to the formation of a regulated polymer chain structure through intermolecular repulsion or attraction. An advantage of these polymer-based methods over other methodologies developed mainly for low-molecular-weight compounds based on the accumulation of relatively weak forces is that molecular orders formed along a polymer chain are generally stable due to covalent bonds. Moreover, using a polymer chain, a very tight or close packing of molecules (monomeric units), which is not plausible for the method based on weak intermolecular attractions, is possible when the enthalpy gain in covalent bond formation by polymerization or by polymer reaction outweighs the loss in free energy in packing molecules tightly into a small space around the polymer chain.Although these polymer-based methods generally require more synthetic efforts than intermolecular-force-based methods, a wider variety of molecular orders may be possible on the basis of re...

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