Substituent Effect on the Electronic Structure and UV/Vis. Spectroscopic Properties of Polyacetylene Oligomers for Photovoltaic Devices: DFT and TD-DFT based investigations

Abstract Due to their promising opto-electronic properties, donor-π-acceptor (D-π-A) organic molecules have emerged as novel class of semiconducting photovoltaic materials. In this paper, we present a systematic study of substituent effect on electronic and absorption properties of the trans-polyacetylene oligomers, H-(CH=CH)n-H (n = 1, 2,······,13), as a function of the π-conjugation length. The HOMO-LUMO gap energies and maximum absorption wavelength (λmax) values of the oligomers connected to the donor and acceptor types of the substituents with varied π-conjugation length are correlated on the basis of the DFT and TD-DFT methods respectively. A non-linear behaviour of change in λmax with and without substituent as a function of n is observed. It is believed that such study can help to design D-π-A compounds for optoelectronic applications.