Design and evaluation of indacenothienothiophene based functional materials for second and third order nonlinear optics properties via DFT approach

Nonlinear optics (NLO) is a fascinating field that explores how intense light interacts with matter. Organic chromophores are regarded as promising materials for nonlinear optics research due to their properties i.e., easy of process, structural versatility, and instant response to NLO effects. Therefore, in current research, a comprehensive investigation was carried out on a series of organic indacenothienothiophene (ITT) based chromophores (AOR and AO1-AO6) to explore their NLO properties through quantum chemical calculations. The DFT and TD-DFT methods at M06/6-311G(d,p) level were employed to investigate the optoelectronic properties of new designed compounds. The parent compound, i.e., AOIC was taken for the designing of the reference molecule (AOR) by substituting one terminal acceptor with donor in AOIC to develop push-pull architecture. The other derivatives (AO1-AO6) were designed via modulation of end-capped acceptor of AOR with benzothiophene (BT) based acceptors. These investigations revealed a red-shift absorption spectra (λ_max = 783-848 nm) with reduced HOMO-LUMO energy gap (E_gap = 1.741-1.956 eV) in AO1-AO6 as compared to AOR (E_gap = 2.040; λ_max=743 nm) in chloroform. Significant charge transferred from donor to BT acceptors through ITT core in AO1-AO6 as illustrated by DOS, FMOs and TDM analyses. All entitled compounds (AO1-AO6) exhibited a notable NLO response relative to the AOR. Particularly, AO2 displayed the prominent results like < α > = 2.790 × 10^-22 esu, β_total = 7.027 × 10^-27 esu and γ_total = 11.440 × 10^-32 esu among all the derivatives. This might be owing to unique optoelectronic characteristics such as lowest E_gap (1.741 eV) and hardness (0.871 eV) with highest softness (0.574 eV) and absorption spectrum (820 nm) of AO2. Hence, these calculations illustrated that the end-capped substitution of acceptor moieties with BT acceptors and the incorporation of conjugated donor system played a vital role in improving the NLO aptitude. Overall, these ITT-based derivatives can be considered as potential materials for promising applications in NLO field.