Correlating the charge density and structural fabrication of new organic dyes to create visible light harvesting materials with tunable NLO refining: insights from DFT

In this investigation, the new organic dyes (TDBR1–TDBR6) have been designed from a moiety, namely thienobenzodithiophene (TDB), using the density functional theory (DFT) approach. The dyes were analyzed to predict their absorption spectra (λ_max), optimized geometries, optical features, density of states, electrostatic potential surfaces with solar cell parameters. It was determined that how electron-donating and electron-withdrawing groups could be affixed with molecules to affect their charge transfer (CT) as a Pull–Push phenomenon. All the new dyes demonstrated a significant Pull–Push effect having maximum absorbance (λ_max) 677–691 nm. Furthermore, the analysis of their bond lengths with respect to their planarity patterns indicated a facile CT patterns. All the new dyes also possessed higher LUMO energies (E_LUMO) than TiO₂ oxide conduction band while they have binding energy (E_b) range of 0.20–0.54 eV. The linear polarizability (< α >) values for all the designed dyes were recorded to be 0.77–1.87 × 10^–21 e.s.u, while their first-order polarizability (β_tot) and second-order hyperpolarizability (γ_tot) were ranged to be 2.21–3.81 × 10^–25 and 13.8–29.3 × 10^–30 esu. Also their computed dipole moments (µ_tot) were in accordance with their NLO responses having their ranges (0.14–7.65 D). The global reactivity parameters had a direct relationship with NLO qualities. They showed their ionization potential values to 0.63–1.87 eV while their softness values (σ) 0.18–1.08 eV. The higher NLO parameters were seen with a reduction in HOMO–LUMO gaps (HLG) which stated that a dye molecule with a lower HLG value might supposed their global reactivity to be softer, less stable, and much more reactive. Their light harvesting efficiency (LHE), with TDB as donor material, was also very promising (−2.8–1.24) having an ON state for dyes TDBR3–TDBR6. Finally, before synthesis, determining material characteristics using DFT will aid in understanding their projected behavior for their applications like NLO and/or as organic dyes.