Reactivity of low energy excited states: Mechanistic and exploratory organic photochemistry

The photochemistry of 3 - methyl - 3 - (1' - naphthyl) -1 - butene was investigated. Direct irradiation led to 1,1 dimethyl - 2 - (1' - naphthyl)cyclopropane as a primary photoproduct and 2 - methyl - 4 - (1' - naphthyl) - 1 - butene as -a secoandary product. The quantum yield for the formation of the cyclopropane was 0.037. The corresponding triple reaction was less efficient, with a quantum yield of 0.012, but still afforded the same product. The excited single rearragement rate was determined by single photon counting; this proved to be ¹k_XXX = 5.9 × 10⁵ sec^-1.The total rate of S₁ decay was determined as 1.59 × 10⁷ sec^-1 with a lifetime of 62.9 nsec.Thus, the lifetime of this rearranging system is quite simiar to that of simple 1-alkylnaphthalenes (Ca 65 nsec); and, the rate of di-π-methane rearrangement is the slowest known. Finally, the rate of radiationless decay of the singlet was found to be almost temperature independent between room temperature and 77 K.