ground state to the defect state. Therefore the knowledge of the IR spectra of these molecules can facilitate future investigations in understanding the unidentified IR emission bands. To study the (5, 7)-membered ring defects in other PAH molecules is believed to be an important step to a significant understanding of the UIR bands and the IR spectra of PAHs, although the defects in astronomical PAH molecules will be extremely difficult to detect with current instruments and tools. But future telescopes and instruments are promising a chance towards the observability of these molecules and their defects. High resolution IR spectrographs of the European Extremely Large Telescope (E-ELT) type telescopes will allow a spatial and wavelength segregation from telluric lines in even highly obscured wavelengths domains (e.g., METIS-IFU with a spectral resolution of R $\sim$ 100 000, Brandl et al. ([@brandl])). The James Webb Space Telescope (JWST) will allow to complete studies of the bright stars observed the IR with extremely high S/N ratios(e.g., MIRI at the JWST, Wright et al.[@wright]).

S.[Ö]{}. and S.E.H. acknowledge support by the Austrian *Fonds zur Wissenschaftlichen Forschung, FWF* DK$+$ project Computational Intersiciplinary Modelling W1227-N16. This work was supported by the Austrian Ministry of Science BMWF as 