Pulse Mode Product-Yield-Detected ESR on the Photoreduction of Anthraquinone in SDS Micellar Solution: Reaction Control by a Microwave Pulse

Abstract

Abstract A pulse mode PYESR (Product-Yield-Detected ESR) spectrometer was developed by using an excimer laser and a TWT microwave amplifier as the components. The effect of ESR transition of the transient radical pair on the yield of the spin adduct of one of the component radicals was observed at a high microwave power of up to 16 W without microwave heating of the solvent. The spin adduct yield of the SDS radical in the photoreduction of anthraquinone in SDS micellar solution initiated by a laser pulse of 308 nm was modulated by up to 45% by a microwave pulse of 10 μs with a peak power of 16 W, which is resonant on the ESR transition of the transient anthrasemiquinone radical. The ESR spectrum of the radical pair was obtained by tracing this modulation as a function of the magnetic field, under which the photoreaction occurred. From the dependence of the product yield on the microwave pulse duration, we could obtain a time profile of the appearance of the transient radical pair.