LED based NMR illumination device for mechanistic studies on photochemical reactions--versatile and simple, yet surprisingly powerful.

An LED based illumination device for mechanistic studies on photochemical reactions by means of NMR spectroscopy is presented. The LEDs are directly switched by the NMR spectrometer with the help of a one-stage electronic circuit. This allows for continuous or alternatively pulsed operation of the LEDs. Continuous operation provides direct comparability with conditions in synthetic chemistry, in pulsed operation the short time light power can be enhanced ninefold. The LEDs are efficiently coupled to a 1000 μm core optical fiber guiding the light into the spectrometer by simply bringing it in close contact to the fiber. The tip of the fiber is roughened by sandblasting and thus emits light in a uniform and efficient way over the full length of the receiver coil. The combination of these techniques tremendously increases the amount of light brought into the NMR sample and makes LEDs an easy, versatile and handy light source for the in situ illumination of NMR samples allowing even for single millisecond time resolved Photo-CIDNP spectroscopy.