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

Abstract 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 ( Φ R = 0.37). Irradiation of 2 in non-degassed ethanol solutions at 285 nm gave colored solutions. The reaction was found to be inefficient ( Φ R = 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.