Spectroscopic and photochemical properties of some annulated boldine derivatives

The aim of this study was to determine the influence of the substituent groups on the photostability of eight boldine derivatives, including some oxazole and oxazinone derivatives, in order to increase the sunscreen protection properties previously demonstrated for boldine. Such derivatives showed bands similar to those of boldine in the absorption and emission spectrum. The spectroscopic properties are pH dependent. The photostability of the derivative compounds was higher than that of boldine, in accordance with the low value of the photoconsumption quantum yield determined. The low fluorescence quantum yield values observed for boldine 1 and 4 as both base and hydrochloride derivative compounds led us to postulate that these compounds are deactivated by a mechanism different to the fluorescence pathway, probably due to the electron-withdrawing inductive effect of NO for boldine 1, and to the increase of the aromatic framework for boldine 4.