The decoration of Li, Na, K, Be, Mg and Ca metal atoms on C$_{20}$ fullerene was studied using the density functional theory (DFT) method. It was shown that the structure of the fullerene was intensely affected by the metal atompresent. All metal atoms have exothermic adsorption on C$_{20}$ fullerene, while Be has the highest value of adsorption energy, enthalpy and free energy. The presence of the metal atom also has a slight effect on Eg while the lowest value of Eg was obtained for Ca@C$_{20}$. The calculations of polarizability and the first hyperpolarizability show that the metal atoms highly influence fullerenes. Among metal atoms, Ca atom had the highest effect and the other metal atoms led to an increase of the first hyperpolarizability to a value of approximately 42000 a.u. The time-dependent (TD)-DFT studies showed that Ca@C$_{20}$has the lowest excitation energies which is in agreement with the calculated first hyperpolarizability.

This study was aimed at investigating the effect of electron donor and acceptor groups on electrical and optical properties of pi-conjugated [26] annulene. The results of the study showed that almost all selected substitutions reduced the value of $E_{\rm g}$ compared with pristine annulene. Calculated dipole moments for the sandwiched forms of annulene are noticeably greater than those of its pristine form, of which the ED2–ANN–QB2 had the maximum value for dipole moment. It was found that the influence of electron donor and acceptor groups on annulene optical properties is very significant. Moreoptical activity improvement was seen in the case of using QB2 and QB3 in one side and other electron donor groups in opposite side of [26] annulene molecule. The higher optical activity of these sandwiched molecules corresponds to higherelectron transfer in them. The results of this research may be useful in designing new photosensitizers.

In this research, different number of the 4,4-difluoro-4-bora-3a,4a,8-triaza-s-indacene (aza-BODIPY) molecule has been employed to design novel oligomers with considerable electrical and optical properties. The geometriesof the designed oligomers were optimized and the IR frequency and cohesive energy were calculated to study their stability. To explore their electronic properties, the HOMO, LUMO energies and $E_g$ of designed oligomers were calculated. It was shown that by enlarging the size of oligomer and increase in number of aza-BODIPY units in designed oligomers, their $E_g$ was narrowed. Finally, it was found that as the numbers of aza-BODIPY units in the oligomers increased, a great enhancement in optical properties was observed. Significant optical properties with strong absorption lines were seen in the visible and near-infrared regions for designed oligomer with six and seven aza-BODIPY units.