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Multifrequency EPR spectroscopy provides detailed information on radicals and radical pairs occurring in photochemical reactions. An important example is spin polarization delivering information about the structure, motional dynamics, and spin-controlled chemistry of transient doublet- and triplet-state radicals as well as radical pairs in disordered systems. To illustrate this, we report here on EPR and ENDOR experiments of UV-irradiated quinone and ketone compounds in liquid alcohol solutions that exhibit pronounced electron and nuclear spin polarization effects (CIDEP and CIDNP, respectively). These experiments were performed jointly by members of the Möbius group from Berlin and Renad Sagdeev from Novosibirsk, when he visited the Department of Physics of Free University Berlin back in 1983. Over the years, this initial Berlin-Novosibirsk cooperation developed into a collaboration of six groups located in Novosibirsk, Kazan, Moscow, Bologna, Berlin, and Mülheim (Ruhr), recently augmented by a seventh group in Dortmund. The efforts are focused on light-induced electron transfer in donor-acceptor complexes in natural and artificial photosynthesis, i.e., processes that are functionally controlled by weak cofactor-matrix hydrogen bonds. These processes require advanced multifrequency and multiresonance EPR techniques to be characterized. [ABSTRACT FROM AUTHOR]