Optically detected magnetic resonance (ODMR) of photoexcited triplet states

Optically Detected Magnetic Resonance (ODMR) is a double resonance technique which combines optical measurements (fluorescence, phosphorescence, absorption) with electron spin resonance spectroscopy. After the first triplet-state ODMR experiments in zero magnetic field reported in 1968 by Schmidt and van der Waals, the number of double resonance studies on excited triplet states grew rapidly. Photosynthesis has proven to be a fruitful field of application due to the intrinsic possibility of forming photo-induced pigment triplet states in many sites of the photosynthetic apparatus. The basic principles of this technique are described and examples of application in Photosynthesis are reported.