Photoswitching of Diazocines in Aqueous Media.

We present a systematic investigation of the photophysical properties of diazocines in aqueous media. The Z-E photoconversion yields of CH2CH2- and CH2S-bridged diazocines decrease with increasing water content in acetonitrile. However, there is one exception. A CH2-NAc-bridged diazocine mostly retains its photostationary state in water (85 to 72%) because of the high quantum yields for the Z → E conversion. Moreover, it is water-soluble without further substitution and is therefore ideally suited as a photoswitch in biological (aqueous) environments.

A versatile method for the determination of photochemical quantum yields via online UV-Vis spectroscopy.

We have developed a simple method for determining the quantum yields of photo-induced reactions. Our setup features a fibre coupled UV-Vis spectrometer, LED irradiation sources, and a calibrated spectrophotometer for precise measurements of the LED photon flux. The initial slope in time-resolved absorbance profiles provides the quantum yield. We show the feasibility of our methodology for the kinetic analysis of photochemical reactions and quantum yield determination. The typical chemical actinometers, ferrioxalate and ortho-nitrobenzaldehyde, as well as riboflavin, a spiro-compound, phosphorus- and germanium-based photoinitiators for radical polymerizations and the frequently utilized photo-switch azobenzene serve as paradigms. The excellent agreement of our results with published data demonstrates the high potential of the proposed method as a convenient alternative to the time-consuming chemical actinometry.