  Polycyclic Aromatic Hydrocarbons (PAHs) are carbon-based molecules that are
ubiquitous in a variety of astrophysical objects and environments. In this
work, we use JWST/MIRI MRS spectroscopy of three Seyferts to compare their
nuclear PAH emission with that of star-forming regions. This study represents
the first of its kind using sub-arcsecond angular resolution data of local
luminous Seyferts (Lbol>10^44.46 erg/s) on a wide wavelength coverage (4.9-28.1
micron). We present an analysis of their nuclear PAH properties by comparing
the observed ratios with PAH diagnostic model grids, derived from theoretical
spectra. Our results show that a suite of PAH features is present in the
innermost parts (~0.45 arcsec at 12 micron; in the inner ~142-245 pc) of
luminous Seyfert galaxies. We find that the nuclear regions of AGN lie at
different positions of the PAH diagnostic diagrams, whereas the SF regions are
concentrated around the average values of SF galaxies. In particular, we find
that the nuclear PAH emission mainly originates in neutral PAHs. In contrast,
PAH emission originating in the SF regions favours ionised PAH grains. The
observed PAH ratios in the nuclear region of AGN-dominated galaxy NGC 6552
indicate the presence of larger-sized PAH molecules compared with those of the
SF regions. Therefore, our results provide evidence that the AGN have a
significant impact on the ionization state (and probably the size) of the PAH
grains on scales of ~142-245 pc.
