Polycyclic aromatic hydrocarbons (PAHs) are one of the most interesting components of the interstellar medium (ISM). But different from laboratory - the isolation of a single species is not possible. The spectra contain a superposition of many different molecules. Therefore a sophisticated understanding of all possible subtypes is required. We present an investigation of the IR spectra of PAHs containing (5, 7)-member ring defects. Using density functional theory, the influence of those defects on the IR spectra of coronene (C 24 H 12) and pyrene (C 16 H 10) and their cations and anions were examined in detail. Additionally, the potential energy surface of the neutral species is explored and an alternative formation pathway is taken into account.