PHOTOLYSIS OF BIS(METHOXYPHENYL) METHYLPHOSPHONATES

On UV irradiation in methanol, bis(methoxyphenyl) methylphosphonates u ndergo ipso coupling of two methoxyphenyl groups or intramolecular rea rrangement of a methoxyphenyl group to give dimethoxybiphenyl and trim ethoxybiphenyl respectively. They exhibit two emission bands attribute d to a monomeric excited methoxyphenyl group and an intramolecular exc imer. 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 ma y be formed through a non-polar intramolecular excimer, while trimetho xybiphenyl may be formed through a polar excimer or a monomeric excite d state. The reactivities also depend on the position of the methoxyl group and decrease in the order 4->3->2-methoxyphenyl.