Enhanced intersystem crossing and transient electron spin polarization in a photoexcited pentacene–trityl radical by Avalos, CE, Richert, S, Socie, E, Karthikeyan, G, Casano, G, Stevanato, G, Kubicki, DJ, Moser, JE, Timmel, CR, Lelli, M, Rossini, AJ, Ouari, O, Emsley, L