LAUSR

Density functional theory (DFT) and time dependent DFT (TD-DFT) calculations were carried out for the oligomers of 3, 4- Ethylenedioxythiophene –Aniline (EDOT-Ani), 3, 4-Ethylenedithiafurane- Aniline (EDTF-Ani) and Thieno [3,4-b] benzene-Aniline (PITN-Ani). Structural parameters, electrical conductivity, spectral properties and electronic properties like ionization potential (IPs), (EAs), HOMO-LUMO isosurfaces and energy gaps of EDOT-Ani, EDTF-Ani and PITN-Ani were calculated and compared using density functional theory at B3LYP/6-31G(d) level which has been successful in predicting trends in conjugated systems. EDOT-Ani results show good correlation with our previous experimental data. The vibrational frequencies with their assignments are also in close agreement with experimental frequencies. The UV-vis spectra are simulated with TD-DFT/6-31G(d) level of theory and the Maximum wavelength (λmax), optical band gap (Egopt) and oscillator straight (f) of three oligomers were compared with each other and with experimental values. Among the studied copolymers, PITN-Ani shows the narrowest band gap which is attributed to its higher donor acceptor property compared to two other polymers.