The indirect technique of electron paramagnetic resonance (EPR) spectroscopy has been employed to examine the role of photogenerated electrons in the studied reacting systems. To this aim, methylviologen dication MV 2+ , a viologen derivative, has been employed. As it is a well-known electron scavenger , its reduction from diamagnetic MV 2+ to paramagnetic MV •+ radical anion can be monitored by EPR spectroscopy.