Mechanisms of Photochemical Degradation in Xanthene Laser Dyes.

7-Azabicyclo[2.2.1]heptane as a Unique and Effective Dialkylamino Auxochrome Moiety: Demonstration in a Fluorescent Rhodamine Dye

“…To test this hypothesis, we evaluated the photostabilities of 221SR and TMSR using relatively innocuous trifluoroethanol as solvent. Because preliminary studies in our laboratory and by others 11,12 found several tetramethylrhodamine derived dyes to be extremely resistant to photodegradation under aerobic conditions, our stability studies were conducted in a mildly alkaline, anaerobic environment, conditions designed to accelerate the photo-oxidative decomposition of the dyes; 13,14 illumination was provided by a 1.7 W, 514 nm CW laser. As is evident from inspecting Figure 3, 221SR is considerably more stable than TMSR; the former dye loses only a small amount of optical density at its absorption maximum without changing color during 30 min of intense illumination while, under identical conditions, the latter undergoes a dramatic decrease in its absorption maximum and a concomitant significant blue shift which is attributable to oxidation-induced demethylation.…”