dComparing Stern-Volmer plots of the S, state lifetime and the fluorescence intensity with a concentration dependence of the time-resolved EPR (TREPR) spectra of the N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD)/maleic anhydride (MA) in 2-propanol system, we have estimated contributions of the complexation between TMPD and MA to the spin polarization observed in the TREPR spectra. The triplet mechanism is operative for the radical ion pair originated from the excited state of the complex, while the radical ion pair formed via the dynamic quenching of the TMPD fluorescence plays important role in the radical pair mechanism. (c) 2007 Elsevier B.V. All rights reserved.