A mechanistic study of photodecomposition of acenaphthylene on a dry silica surface

The photochemistry of acenaphthylene (AC) has been studied on a dry silica surface at very low coverages (less than 10% of a monolayer) under aerated conditions. Adsorption of AC onto silica surface from cyclohexane follows a Freundlich adsorption isotherm, demonstrating a range of weak interactions between AC and the surface active sites. Photolysis of AC at the solid-air interface led to the formation of photo-oxidation products formed via the addition of singlet molecular oxygen to ground-state AC, and photodimers (cis and trans). The oxidation products include 1,2-acenaphthenedione (1), 2-hydroxy-1-acenaphthenone (2), 1,8-naphthalenedicarboxaldehyde (3) and 1,8-naphthalic anhydride (4). The yield of dimers increases as the surface coverage is raised. Both the excited singlet state and the excited triplet state of AC are involved in the observed dimerization on the surface.