Photochemical study of 4-(4,9-dimethoxy-2,11-n-dipropyl-6,7-dihydro-5,8-dioxa-dibenzo[a,c]cycloocten-6-yl)-2-methoxyphenol, a lignin model of phenolic dibenzodioxocin unit

The photochemical behavior of compound 2 was studied as lignin model of phenolic dibenzodioxocin, due to the presence of photoreactive α-O-4, β-O-4 linkages and phenolic group. The latter, very sensitive to oxidation, should increase the dibenzodioxocin photoreactivity compared to the non-phenolic dibenzodioxocin lignin model 1 (ΦR = 0.37). Irradiation of 2 in non-degassed ethanol solutions at 285 nm gave colored solutions. The reaction was found to be inefficient (ΦR = 0.015). Analysis of the photoproducts by mass spectrometry suggests that reversible formation of an intermediate quinone-methide, by α-O-4 bond cleavage, might account for the low quantum yield value. The short wavelength fluorescence emission observed for compound 1, compared to that of biphenylbiphenol 4, was also found in molecule 2, confirming the important role played by the dibenzodioxocin ring in the fluorescence emission of these structures.