Abstarct: Todays, polythiophene, as one of the conducting polymers, received great attention in the research and investigation centers due to use in a variety of devices, including nonlinear optics, Schottky diodes, organic light-emitting diodes (OLEDs), thin-film field-effect transistors (FETs), and etc. In this thesis, a series of oligothiophenes including mono-, di-, tri-, tetra-, penta-, hexa-, hepta- and octamers that terminated with alkyl amines group at the end-side of the chain, are investigated. The quantum calculations were used to study the structural and electronic properties of studied oligomers with two different methods including the density functional theory and Hartree-Fock methods in which the density functional theory in B3LYP/6-31G** level of theory was selected as the best method. Investigation of structural properties of oligothiophenes shows that the torsional angles of (amino alkyl end-capped oligothiophenes) are smaller than non-substituted oligothiophenes and they are closer to planar structure. Also in amino alkyl end-capped oligothiophenes, the length of single bond (C-C) and double bond (C=C) in π-conjugated system are closer to each other which represents an improvement in π-conjugated oligomeric chain. Results show that energy gap in alkyl amine-capped oligothiophenes decreases. TD-DFT calculations and the study of the UV-Vis spectra of oligothiophenes that closed with alkyl amine groups, indicate a decrease in the excitation energy respect to the non-substituted oligothiophenes. Furthermore, closing the end-side of oligothiophenes chain by alkyl amine groups cause to ease the hole injection. The energy of charge transition in closed oligothiophene with alkyl amine substituent, increased than non-substituted oligothiophenes which represents the charge delocalization in the oligomeric chain. The study of spin density distribution along the conjugated chain of alkyl amine-capped oligothiophenes and also Mullikan charge distribution on each thiophene ring of oligomer, indicate an improvement in charge transition. The study of the charged oligomeric species show that both radical cation and radical anion show better conductivity than the neutral species. In the other word, the amino alkyl end-capped polythiophenes at the doped state could have higher conductivity.