Polycyclic Aromatic Hydrocarbons (PAHs) are a cornerstone of interstellar physics and chemistry. They play a fundamental role in heating the interstellar medium (ISM) through the photoelectric effect, regulating its ionization balance, and contributing to its molecular complexity. Identified as the carriers of the aromatic infrared bands (AIBs), PAHs are detected across a vast range of astrophysical environments—from the ISM of our own Galaxy to the early universe. In addition to their role in the ISM, PAHs serve as critical tracers of star formation in galaxies across cosmic time and as sensitive probes of physical conditions in planet-forming disks. Their detection in a variety of solar system objects has also made them central to discussions of astrobiology and the origin of prebiotic organics. 

With JWST’s unprecedented combination of spectral resolution, spatial detail, and sensitivity, the study of aromatics has entered a transformative era. JWST enables resolved studies of the evolution of aromatic species in nearby interstellar environments while simultaneously detecting AIBs and the UV attenuation bump at high redshifts, fueling an explosion of extragalactic research using PAHs as tracers of star formation, dust processing, and galaxy evolution.  

Yet, many fundamental questions about the life cycle of PAHs and fullerenes remain unanswered: How do these molecules form and survive under the extreme conditions of space? How do their physical and chemical properties transform over cosmic time? What roles do they play in shaping the lifecycle of interstellar matter? Laboratory experiments and quantum chemical calculations are essential to address these questions, enabling robust interpretation of observations and identification of molecular structures and processes. A comprehensive understanding of interstellar aromatics also requires connecting them to other spectral signatures, including the diffuse interstellar bands in the optical and the radio detections of small PAHs in cold molecular clouds.

This symposium will bring together experts from observational astronomy, laboratory astrophysics, theoretical modeling, and quantum chemistry to explore the latest discoveries and future frontiers in PAH and fullerene research. With a special emphasis on extragalactic PAH studies, we will discuss how new observational capabilities (e.g., JWST, SPHEREx) and cutting-edge theoretical and experimental approaches can expand our understanding of these key interstellar species.

The meeting is the fourth installment in a series of international symposia on interstellar PAHs, following previous editions in Toulouse (2010), Noordwijk (2016), and Aarhus (2022).