Photochemical and photophysical studies of bicyclo[4.3.0]non-1(6)-en-2-one

The properties of the lowest excited triplet state of bicyclo[4.3.0] non-1 (6)-en-2-one (BNEN) have been investigated by nanosecond transient absorption spectroscopy, photoacoustic calorimetry, measurements of 1 O 2 quantum yields, and photochemical studies in solution. Both the lifetime (1.4 μs) and the energy (74-76 kcal mol -1 ) of the BNEN triplet reflect its exceptional conformational rigidity, which prohibits relaxation along the 3 (π,π * ) potential energy surface by twisting around the C=C bond