Interaction between Polarized Triplets and Stable Radicals in Liquid Solutions

The magnetization generated by the interaction of stable radicals with photoexcited triplets in a viscous solution at room temperature was measured by light-induced Fourier transform electron paramagnetic resonance spectroscopy (FT-EPR). High and long-lived polarized magnetization (>100 μs in emission) is generated in the stable radical (α,γ-bisdiphenylene-β-phenylallyl) interacting with the photoexcited triplet state of free base, and Zn, tetraphenylporphyrin. Radical-triplet interaction was analyzed quantitatively employing a combined model of electron spin polarization transfer (ESPT) and radical−triplet pair mechanism (RTPM). The presented model allows calculating the radical polarization following an encounter with a thermal or nonthermal triplets. Moreover, an important conclusion from this study is that the generation of radical polarization via RTPM does not require efficient quenching of the photoexcited triplet.