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

Thephotochemical reaction of 3(3)](1,3,5)cyclophane 2, which is a photoprecursor for the formation of propella3(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, tetracyclo6.3.1.0.(2,7)0(4,11)]dodeca-5,9-diene 43, hexacyclo6.4.0.0.(2,6)0.(4,11)0.(5,10)0(9,12)]dodecane 44, and pentacyclo6.4.0.0.(2,6)0.(4,11)0(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 3n]cyclophanes (3n]CP, n = 2-6) were investigated by measuring the emission spectra and determining the quantum yields and lifetimes of the fluorescence. All 3n]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 3n]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.