9,10-Di(1-naphthyl)phenanthrene (5 a) and 9,10-di(2-naphthyl)phenanthrene (5 b) have been synthesized. It is shown that 5 a and 5b both form two stable rotational (cis/trans) isomers with the naphthalene molecular planes perpendicular to the phenanthrene plane. In the case of 5 a the mixture of the two isomers has been separated in a preparative scale and each isomer characterized by e. g., NMR spectroscopy. Photocyclization of 5a leads to benzo[e]phenanthro[1,2,3,4-ghi]perylene (9) while 5 b yields phenanthro[9,10-i]pentahelicene (14); both hydrocarbons have not been previously described in the literature. The observed selectivities of photocyclization are explained on the basis of the structures and stabilities of the initially formed photoproducts (dihydro structures 15 and 14 a). The role of intramolecular non-radiative singlet-singlet energy transfer (naphthalene → phenanthrene) as competing with photocyclization is discussed in detail.