The ability to generate well-defined states with large electron spin polarization is useful for applications in molecular spintronics, high-energy physics and magnetic resonance spectroscopy. Pentacene-radical derivatives can rapidly form triplet excited states through enhanced intersystem crossing and under the right conditions this can in turn lead to polarization of the tethered radical . The magnitude of the spin polarization on the radical substituent depends on many factors: local magnetic and electric fields, molecular geometry, and spin-spin coupling [2-4]. In this work we present time resolved electron paramagnetic resonance (TREPR) and field swept echo detected electron paramagnetic resonance (FSEPR) measurements on three pentacene derivatives with trityl, BDPA or TEMPO substituents. We observe polarization transfer between the pentacene excited triplet and the TRITYL radical, but do not observe the same for the BDPA and TEMPO derivatives. We also investigate polarization transfer in the pentacene-TRITYL system in different glassy environments and observe distinct polarization transfer behavior depending on the solvent used. We explain the TREPR and FSEPR measurements by comparing the excited-state dynamics of the three pentacene derivatives from nanosecond and femtosecond transient absorption measurements. We observe a two order of magnitude difference in the timescale of triplet formation of the pentacene TRITYL system when compared to the pentacene with the BDPA and TEMPO substituents.
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