Competing excited state intramolecular proton transfer pathways from phenol to anthracene moieties.
Four new 9-(2'-hydroxyphenyl)anthracene derivatives 7-10 were synthesized and their potential excited state intramolecular proton transfer (ESIPT) reaction investigated. Whereas 7 reacted via the anticipated (formal) ESIPT reaction (proton transfer to the 10-position of the anthracene), derivatives 8-10 reacted via ESIPT to both 9- and 10-positions, giving rise to two types of intermediates, quinone methides (e.g., 29) and zwitterions (e.g., 30). These intermediates are trapped by solvent (water or methanol) giving addition products that can readily revert back to starting material. However, on extended photolysis, the products that are isolated can best be rationalized as being due to competing elimination and intramolecular cyclization of zwitterions 30 and 37. These results show that it is possible to structurally tune ESIPT in (hydroxyphenyl)anthracenes to either result in a completely reversible reaction or give isolable anthracene addition or rearrangement products.
Department of Chemistry, Box 3065, University of Victoria, British Columbia, Canada V8W 3V6.
Nikola
N
Basarić
Peter
P
Wan