The research in the (thieno[3,4-b]pyrazine, TP) Ï€ -conjugated molecules has become onernof the most interesting topics in the fields of chemistry. The use of low band gap materialsrnis a viable method for better harvesting of the solar spectrum and increasing itsrnefficiency. The control of the band gap of these materials is a research issue of ongoingrninterest. In this work, the geometrical and electronic properties of (Thieno[3,4-rnb]pyrazine, [TP]) based donor-acceptor conjugated oligomers were studied by therndensity functional theory (DFT) at the B3LYP level with 6-31G (d,p) basis set from therngeometry optimization the inter-rings bonds are longer than normal double bonds butrnshorter than the single bonds these indicate that the emerging of a quinoidal likerndistortions as a result of oxidation. A low band gap will be expected in polymersrncontaining donor-acceptor (D - A) repeating units. The absorption spectra of a designedrnlow-band gap conjugated polymer has been studied using the TDDFT/B3LYP/6-31G.rnTwo main absorption peaks can be seen, the one largest in wavelength corresponding torna HOMO to LUMO transition, except compound C1 and one involving higher orderrnexcitations. The thermodynamic property calculations show that up on polymerization thernchange in thermodynamic properties decreases. This decrease in change inrnthermodynamic properties shows that the oxidized forms of the compound (C1) isrnunstable with compare to other compounds.rnKeyword/phrases: Thieno[3,4-b]pyrazine(TP), donor-acceptor, low-band gap,rnoptoelectronic, DFT, geometrical and electronic properties