Photochemical sudy of [33](1,3,5)cyclophane and emission spectral poperties of [3n]cyclophanes (n=2-6)

Thephotochemical reaction of [3(3)](1,3,5)cyclophane 2, which is a photoprecursor for the formation of propella[3(3)]prismane 18, was studied using a sterilizing lamp (254 nm). Upon photolysis in dry and wet CH2Cl2 or MeOH in the presence of 2 mol/L aqueous HCl solution, the cyclophane 2 afforded novel cage compounds comprised of new skeletons, tetracyclo[6.3.1.0.O-2,7(4,11)]dodeca-5,9-diene 43, hexacyclo[6.4.0.0.O-2,O-6.O-4,O-11.O-5,10(9,12)]dodecane 44, and pentacyclo[6.4.0.0.O-2,O-6.O-4,11(5,10)]dodecane 45. All of these products were confirmed by the X-ray structural analyses. A possible mechanism for the formation of these photoproducts via the hexaprismane derivative 18 is proposed. The photophysical properties in the excited state of the [3(n)]cyclophanes ([3(n)]CP, n = 2-6) were investigated by measuring the emission spectra and determining the quantum yields and lifetimes of the fluorescence. All [3(n)]CPs show excimeric fluorescence without a monomeric one. The lifetime of the excimer fluorescence becomes gradually longer with the increasing number of the trimethylene bridges. The [3(n)]CPs also shows excimeric phosphorescence spectra without vibrational structures for n = 2, 4, and 5, while phosphorescence is absent for n = 3 and 6. With an increase in symmetry of the benzene skeleton in the [3(3)]- and [3(6)]CPS, the probability of the radiation (phosphorescence) process from the lowest triplet state may drastically decrease.