Nature (Hole or Electron) of Charge-Transfer Ability of Substituted Cyclopyrenylene Hoop-Shaped Compounds

We theoretically investigate here by means of DFT methods how the selective substitution in cyclic organic nanorings composed of pyrene units may promote semiconducting properties, analyzing the energy needed for a hole- or electron-transfer accommodation as a function of the substitution pattern and the system size (i.e., number of pyrene units). We choose to study both [3]­Cyclo-2,7-pyrenylene ([3]­CPY) and [4]­Cyclo-2,7-pyrenylene ([4]­CPY) compounds, the latter already synthesized, with substituents other than hydrogen acting in ipso and ortho positions, as well as the effect of the per-substitution. As substituents, we selected a set of electroactive halogen atoms (F, Cl, and Br) and groups (CN) to disclose structure–property relationships allowing thus to anticipate the use of these systems as organic molecular semiconductors.