Quantum mechanical assessment on the optical properties of capsanthin conformers.

As optical properties, the ultraviolet-visible (UV-Vis) absorption spectra of capsanthin-based red natural dye are a decisive parameter for their usage in various applications. Thus, accurately predicting the maximum UV-Vis wavelength ( λ max $$ {\lambda}_{\mathrm{max}} $$ ) values is critical in designing dye-conjugated material. Extensive metadynamics simulations were carried out to generate capsanthin conformers at various levels of the extended tight-binding method. Benchmarking the time-dependent density-functional theory (TD-DFT) methods help understand the results of a particular functional and allows a comparison between results obtained with different functional. The long-range correction (LC) scheme in LC-TD-DFT-D4/ωB97X/def2-SVP has been found to reproduce the experimental λ max , $$ {\lambda}_{\mathrm{max}}, $$ and exhibited the effect of conformational changes to the calculated wavelengths. On the other hand, an inexpensive yet efficient LC-TD-DFTB method reproduced the experimental λ max $$ {\lambda}_{\mathrm{max}} $$ insensitive to conformational changes.