The photochemistry of l-phenyl-l, 2-dihydronaphthalene (1) in methanol and hexane has been investigated. The lack of influence of solvent polarity and of the presence of sulfuric acid on the rate of formation of exo-4-phenylbenzobicyclo [3.1. 0] hex-2-ene (em-2) from the primary, ring-opened photoproduct cZt-ta of 1 precludes a sudden-polarized, zwitterionic excited state from being involved in the intramolecular [4+ 21 photocycloaddition reaction ...