Wavelength-dependence of Norrish type I cleavage reactions in carbonyl groups of dammar resin triterpenoids and its implications for accelerated aging of organic materials

Abstract

Norrish Type I cleavage reactions of carbonyl groups in dammar triterpenoids were studied using different wavelengths of UV exposure. Films of dammar resin were exposed to xenon arc irradiance, using longpass filters with varying cut-on wavelengths. The results were studied using gas chromatography mass spectrometry of the triterpenoid fraction. It was shown that α-cleavage of carbonyl groups, leading to formation of A-seco compounds, takes place at wavelengths present in daylight filtered by window glass, thus validating the aging method for the study of the stability of materials during indoor exposure. Claims that xenon arc exposure leads to abnormal degradation appear incorrect. By eliminating UV radiation entirely below 400 nm, Norrish reactions are inhibited. These results are of particular relevance in accelerated aging studies in heritage science but also in other fields.