Irradiation of 4-biphenylyl-4-methyl-2-cyclohexenone (5) in benzene or methanol produced trans-6-biphenylyl-5-methylbicyclo[3,1,0]hexan-2-o ne (5a) and 3-biphenylyl-4-methylcyclohex-2-enone (5b). Electronic configurations of the excited states for 5a and 5b were assigned as n, ${pi}^*$ and ${pi}$, ${pi}^*$ triplet states respectively. Irradiation of 4-methyl-4(${eta}$-naphthyl)-2-cyclohexenone in benzene or methanol gave 4-methyl-3-(${eta}$ -naphthyl)-2-cyclohexenone (6a), which is thought to arise from ${pi}$, ${pi}^*$ triplet state.