Photolysis of bis(methoxyphenyl) methylphosphonates

Abstract On UV irradiation in methanol, bis(methoxyphenyl) methylphosphonates undergo ipso coupling of two methoxyphenyl groups or intramolecular rearrangement of a methoxyphenyl group to give dimethoxybiphenyl and trimethoxybiphenyl respectively. They exhibit two emission bands attributed to a monomeric excited methoxyphenyl group and an intramolecular excimer. Their fluorescence spectra and reactivities are affected by the position of the methoxyl group on the benzene ring. The intramolecular excimer of bis(3-methoxyphenyl) methylphosphonate is more polar than that of bis(4-methoxyphenyl) methylphosphonate, because the former has a more unsymmetrical aryl group than the latter. Dimethoxybiphenyl may be formed through a non-polar intramolecular excimer, while trimethoxybiphenyl may be formed through a polar excimer or a monomeric excited state. The reactivities also depend on the position of the methoxylgroup and decrease in the order 4->3->2-methoxyphenyl.