Synergy effect of central ring modification and fluorination on the electronic structure of condensed arenes

A theoretical study of a set of unsubstituted and fluorinated small aromatic monocyclic and arene-type condensed molecules is presented. The quantum chemical calculations were performed at the density functional theory level. The fluorination effect on the Wibberg bond order and structural HOMA indices is discussed for monocyclic and bicyclic molecules with arene units. Changes in the electronic structure in the vicinity of the atoms forming the aromatic ring were analyzed using the sum of negative and positive partial atomic charges. The global electron-rich or electron-deficient character of investigated small molecules was also quantified using vertical ionization potentials and vertical electron affinities. For selected tricyclic and pentacyclic condensed molecules, the synergy of central ring modification and fluorination was investigated for the electrochemical and lowest energy optical band gaps. The geometric pattern of these compounds is either linear or angular, and it is based on possible combinations of benzene moieties with a six- or five-membered central aromatic ring. Theoretical results were compared with experimental data. The obtained data indicate that the fluorinated angular pentacyclic molecules with a central thiophene and pyridazine moiety are expected to be promising candidates for the construction of organic n-type semiconductors with respect to the setting of electronic structure as well as internal reorganization energies.