Extended conjugated -systemsespecially aromatic onesexpress particular reactivity and show the ability to absorb energy in the UV/vis range. To further elucidate the homoaromatic character of 15 we investigated its behavior upon irradiation with light, as has been done for several other homoaromatic compounds . We found that homoannulene ester 15 undergoes a photoinduced rearrangement of the barbaralone framework forming ester 18 (305 nm LED irradiation for 80 sec of a dilute cyclohexane or MeCN solution of 15, Fig. ). The thermal stability of photoproduct 18 was verified by heating the photostationary state (PSS) mixture obtained at 305 nm in MeCN for 9.25 h at 55 °C without any noticeable change in composition (see Supplementary Figures and). Therefore, compounds 15 and 18 could be separated using preparative HPLC chromatography. Full characterization of 18 using NMR spectroscopy and HR-MS analysis allowed the unambiguous determination of its structure.