A comparative theoretical study on the structural, spectral, microtopology exploration (ELF, RDG, IRI, TDM), NBO and nonlinear optical properties of Red170 from different solvents and substituents

The effect of solvents and substituents on the C.I. Pigment PR170, the best known member of the naphthol red family, is investigated. Both PR170 and its alkoxy derivatives were analyzed using FTIR, 1H NMR and UV–Vis spectroscopy. The study included the evaluation of the average local ionization energy (ALIE), MEP, HOMO-LUMO analysis. The nature of intra- and intermolecular contacts in the crystal structure was also investigated using crystal packing and Hirshfeld surface analysis. Covalent and non-covalent interactions in PR170 were comprehensively described by IRI, RDG and ELF. In addition, Natural Bonding Orbital (NBO) and Fukui function calculations were performed. An analysis of the UV–Vis electronic transitions for different solvents was carried out, providing insight into the charge transfer processes within both PR170 and its derivatives. In particular, the research indicated a CT-type excitation at the S2 level during the hole-electron transfer analysis. The NLO results showed that PR170 is a promising candidate for nonlinear optical materials.