Electronic Properties of Branched Molecular Structures. Review
The design of new types of macromolecular architecture is one of the main directions of development of modern polymer physics. With regard to electronics, a special place is occupied by electrically conductive π-conjugated molecules. The review considers the distinctive features of the electronic properties of organic semiconductors in compare with their solid-state analogs. Special attention is paid to the role of electron-electron and electron-phonon interactions in the formation of autolocalized excited states: solitons and polarons. The constructive and destructive interference effects in molecular structures containing branching nodes and ring groups are discussed. The size of a branched molecule should be not large to preserve quantum coherence. The autolocalization effects in such molecules are not pronounced and transport is provided by electrons and holes injected from electrodes. Two main approaches to the description of quantum interference in branched molecules are desribed in the review: on the basis of molecular orbitals and within localized atomic orbitals picture. These approaches make it possible to formulate design rules for molecular structure exhibiting quantum interference. The recent results are presented on the design of quantum interference molecular transistor with extremely low switching power. Dendrimers, tree-branching nonconjugated molecules, are briefly considered, which can become effective tools for electromagnetic radiation collection and transformation.