Photochemistry of 1,5-diaryl-1,5-diketones

• DOI: 10.1021/ja00522a048
• Publication Date: 2005-03-18T17:17:53Z
• Authors: J. P. Bays; M. V. Encinas; R. D. Small; J. C. Scaiano
• Keywords: 01 natural sciences; 0104 chemical sciences

The photochemistry of ketones 1-3 of the structure where 1,R/sup 1/ = R/sup 2/ = H, 2,R/sup 1/ = H; R/sup 2/ = CH/sub 3/, 3,R/sup 1/ = CH/sub 3/; R/sup 2/ = H, has been examined in solution at room temperature by using quantum yield and laser flash photolysis techniques. Triplet energy migration between the two chromophores leads to complete excitation equilibration. In the case of 3, two triplet states have been characterized, reflecting the syn and anti conformation of the o-methylbenzoyl chromophore. The biradicals produced in the triplet decay have lifetimes of ca. 50 ns in wet acetonitrile, for 1 and 2 and 430 ns in the case of 3, where it results from abstraction of the benzylic hydrogens. Biradicals are produced from 2 with a quantum yield of 1.0; however, the product yields are considerably lower, even in polar hydroxylic solvents. The effect is attributed to strong intramolecular hydrogen bonding in the biradical.