Electronic structure of organic biradical molecular films

Most research in the fleld of organic electronics has focused on p-conjugated molecules with a closed-shell configuration, which accommodate their p-electrons in only bonding orbitals and are consequently quite stable. In general, closed-shell molecules have wide energy gaps, and they have significantly weaker intermolecular interactions. In contrast, recently organic biradicals have attracted considerable attention, owing to their interesting physical properties, e.g., a small energy gap and strong intermolecular interactions. Organic biradical molecules are composed of a pair of organic radicals that possess an open-shell configuration. Owing to their radical nature, biradical molecules exhibit unusual physical properties such as those listed above. This article is a review of our recent study on the electronic structure of two different types of organic biradical molecules that have potential as new materials for manufacturing electronic devices. In particular, our results show that organic biradicals are expected to form a new class of materials for use in organic electronics as new building blocks for highly ordered organic semiconducting films with wide energy band dispersion widths and a narrow energy gap.