Low-temperature photooxygenation of(1S,6R)-3-((E,Z) -methoxymethylene)bicyclo [4.4.0] decan-8-one (7), prepared in 10 steps from 2,6-dimethoxynaphthalene (5), yields a mixture of four isomeric 1,2-dioxetanes (8a-d) with ee > 98%. Upon thermal decomposition, these 1,2-dioxetanes are all precursors for 3-((1)n pi*)-(1S,6R)-bicyclo[4.4.0]decane-3,8-dione (1*), an optically active diketone in its locally excited (1)n pi* state. The optical activity of this molecule is evidenced by the nonvanishing circular polarization in the chemiluminescence of 8a-d. The degree of polarization (g(e)) at 420 nm equals -(1.5 +/- 0.3) X 10(-3), a value which is similar to that of the regular fluorescence of optically active (1S,6R,8S)-8-hydroxybicyclo[4.4.0]decan-3-one (6). This similarity implies the absence of substantial racemization in the excited state, whence one concludes that the rate constant for intramolecular (1)n pi* energy transfer in 1* is less than or similar to 10(9) s(-1). The chiroptical results show that localization of excitation energy at the carbonyl at the 3-position of 1* can be achieved by the synthetic route applied, yielding enantiomerically pure 3-((1)n pi*)-(1S,6R)-bicyclo[4.4.0]decane-3,8-dione (1*), an optically active molecule whose chirality is due solely to the presence of localized electronic excitation energy.