In this work,a quantum-chemical investigation on the structural and opto-electronic properties of oligo(thiophene-phenylene) (4TP)is carded out.The results are discussed in comparison with the properties of corresponding oligothiophene(8T)and oligophenylene(8P).As the opto-electronic properties of this type of conducting polymers are governed by their electronic band gap,we shall also present a comparison among HOMO,LUMO and band gap energies of these three materials. In this work, a quantum-chemical investigation on the structural and opto-electronic properties of oligo (thiophene-phenylene) (4TP) is carded out. The results are discussed in comparison with the properties of the corresponding oligothiophene (8T) and oligophenylene As the opto-electronic properties of this type of conducting polymers are governed by their electronic band gap, we shall also present a comparison in HOMO, LUMO and band gap energies of these three materials.