Photochemical reaction of [6]-l, 4-cyclophaneanthraquinone.

[6]-1,4-Cyclophaneanthraquinone (CHAQ) has been synthesized and its photochemical reaction is studied. Nanosecond laser photolysis of CHAQ in EPA at room temperature reveals that both the lowest excited singlet and triplet states of CHAQ cause the intramolecular hydrogen-atom abstraction yielding the 1,4-biradical, i.e., the hydrogenatom abstraction by the carbonyl oxygen from the benzylic methylene of the cyclophane bridge. Since steady-state photolysis of CHAQ in EPA at 77 K reveals the formation of cyclophane-9-hydroxy-1,10-anthraquinone-1-methide ( 2), the results obtained by steadystate photolysis at room temperature are interpreted as follows: (1) In benzene, 2 changes to a naphthoquinone derivative ( 6). (2) In EPA, 2 yields its ethanol adduct ( 3) and there exists an equilibrium between 3 (major) and 6 (minor). (3) By a dark reaction, 3 and/or 6 revert very slowly to CHAQ. [ABSTRACT FROM AUTHOR]