Irradiation of (l,4)-anthracenophane (5) through a solution filter (λ > 350 nm) gave five kinds of cyclobutane dimers 6–10 conjoined at the C1 and C2 of the anthracene core. Neither valence isomerization to the Dewar isomer nor [4 + 4] dimerization at C9 and C10 was observed. The absence of remarkable effect of concentration or solvent polarity on the product distribution suggests that the dimerization of 5, at least leading to the major isomer 9, proceeds through an excited triplet state. Irradiation of 5 through a Pyrex filter afforded dimer 11 as the major product which was derived from the cis-trans dimer 8. This was accomplished by intramolecular hydrogen abstraction from the bridge methylene by the bridgehead double bond of the lower vinylnaphthalene unit followed by transannular coupling of the diradical intermediate. The molecular structures of dimers 6, 8, 9, and 11 were determined by X-ray structure analyses. The most remarkable structural feature of the head-to-head isomers 6, 8, and 11 is the unusual long distance (1.62–1.64 Å) of the cyclobutane bond a (C7–C38). The elongation of this bond in the cis-trans isomers 8 and 11 is ascribed to steric repulsion between the methylene groups across the cyclobutane ring, while that of the cis-cis isomer 6 is ascribed mainly to “through-bond” interaction.