Molecular structure and spectra of danthron and emodin studied by FTIR, Raman spectroscopy and DFT techniques

In this work, experimental and theoretical studies on danthron and emodin are presented. Experimentally, Fourier transform infrared (FTIR), Raman and UV–Vis spectra of danthron and emodin were recorded. The structure and vibrational frequencies of the molecules were calculated using density functional theory (DFT) with the B3LYP functional using the triple zeta (TZVP) basis set. Among various possible structures of danthron and emodin, it was found that the most stable structures involve intramolecular hydrogen bonds between two OH and C=O groups. The theoretical IR spectra of the most stable conformations of danthron and emodin correlate well with their experimental FTIR. Detailed vibrational frequency analysis was done for all the vibrational modes obtained and were assigned to the ring vibrations along with the stretching and bending of specific bond vibrations. The bands obtained from the experimental FTIR and Raman spectra of both the molecules correlate well with their theoretical data.