Enriching the compositional tailoring of NLO responsive dyes with diversity oriented electron acceptors as visible light harvesters: a DFT/TD-DFT approach.

The end-capped modelling of non-fullerene acceptor (NFA) units have been performed onto the structure of a dithiophene-based 6,6′-di(thiophen-2-yl)-4,4′-bipyrimidine (DTB) moiety to design nine new dyes (DTIT1–DTIT9). All the calculations were performed by density functional theory (DFT) and time dependent DFT (TD-DFT) based calculations. Their molecular geometries were optimised to their ground state energies at CAM-B3LYP functional of DFT with 6–31+G(d,p). The maximum absorbance (λ_max) of DTB was noted at 431 nm and all the new dyes DTIT1–DTIT9 displayed λ_max frequencies around 432–498 nm. The natural transition orbital (NTO) analysis has been performed for each dye molecule only for the excited state with the highest oscillator strength (f). The natural bond orbital (NBO) analysis was used to determine the stability of dyes with their greatest hyper conjugation related interactions. All the dyes DTIT1–DTIT9 had smaller HOMO–LUMO energy gaps (E_gaps) than DTB ranging between 0.38 and 5.79 eV, resulting in a significant nonlinear optical (NLO) response. The dye DTIT7 had the highest NLO response of all the compounds studied, owing to the inclusion of four cyanide (CN) groups. NLO activation was higher in the designed substances than in DTB. The dyes DTIT1–DTIT9 may be potential contenders for NLO applications. [ABSTRACT FROM AUTHOR]