Theoretical Studies on the Structural, Electronic and Optical Properties of the New π-conjugated Copolymers Based on Carbazole and Thiophene

Abstract

This work reports a theoretical investigation of π-conjugated oligomers constituted by n units (n = 1-4) based on carbazole and ethylenedioxythiophene. The molecular geometry, torsional potential, electronic and optical properties of the oligomers [Cbz-(Edot)_n-Cbz] (n = 1-4) are investigated using DFT (B3LYP/3-21G*) calculations. The discussion is focused on the influence of chain length on the properties of these copolymers. The analyses of torsional angles for [Cbz-(Edot)₄-Cbz] reveal that the structure has a anti-planar conformation. The electronic properties of the molecules, HOMO, LUMO and E_g (HOMO-LUMO), are studied using B3LYP functional. The results have been compared with those of thiophene and ethylenedioxythiophene. The lowest excitation energies (E_ex) and the maximal absorption wavelength (λ_abs) are studied using the TD/DFT, ZINDO and CIS methods. The electronic transitions of the absorption spectrum derived by TD/DFT method give useful structural and electronic information for designing novel conducting organic polymer materials. The bridging effect by C=C(CN)₂ on the optoelectronic properties of the (carbazole-thiophene-carbazole) comonomer is investigated.

Keywords: Conducting polymer; Carbazole-(Ethylenedioxythiophene)_n-Carbazole comonomers; DFT Optoelectronic properties; absorption coefficient; Bridging effect.

© 2012 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. 

doi: http://dx.doi.org/10.3329/jsr.v4i1.7450

J. Sci. Res. 4 (1), 119-133 (2012)