| The photochemistry of 4,4-dibiphenylylcyclohex-2-en-1-one and 5,5-dibiphenylylcyclohexa-1,3-diene was studied to investigate the effect of having bichromophoric molecules with equal energy chromophores. In the first molecule, both the cyclohexenone and biphenyl moieties have triplet energies ca. 69 kcal/mole, and in the second molecule, both moieties have singlet energies ca. 95 kcal/mole.;For the diene system, up to five photoproducts were formed depending upon the photolysis conditions. The major products under all conditions were trans-5,6-dibiphenylylbicyclo 3.1.0 hex-2-ene and trans-4,5-dibipheylylbicyclo 3.1.0 hex-2-ene. This contrasts with the behavior of the phenyldiene where the major product depended upon the multiplicity of the excited state with the singlet giving electrocyclic ring opening and the triplet giving a di-pi-methane reaction.;Work was also done towards synthesizing molecular "rods" consisting of bicyclo 2.2.2 octane units bonded in a bridgehead to bridgehead manner with three or more "monomer" units. Success in synthesizing a 3 -rod was achieved using a magnesium - nickel(II) chloride promoted cross coupling reaction between bridgehead iodo- i - and 2 -rods, thus giving the first examples of rods greater than two units in length.;For the enone, three products were observed. These were the cis- and trans- isomers of 5,6-dibiphenylylcicyclo 3.1.0 hex-2-one and 3,4-dibiphenylylcyclohex-2-en-1-one. The quantum yields in benzene were 0.33 for the trans- product, 0.019 for the cis- product, and 0.013 for the 3,4-enone. Exothermic sensitization with xanthone (74 kcal/mole) and benzophenone (69 kcal/mole) gave the same quantum yields as the direct photolysis. Stern-Volmer quenching studies were done and gave a straight line. The rate of decay of the quenchable triplet was 5.7 x 10('8) sec('-1), which was 5.5-fold faster than the phenylenone. The operational rate of radiationless decay was 3.6 x 10('8) sec('-1), which was 2.3-fold than the phenylenone. |
