The time-resolved electron spin resonance (TRESR) spectra and chemically induced dynamic electron polarization (CIDEP) phenomena obtained from laser flash photolysis of benzaldehyde (BA) in homogeneous solvent, micellar solutions and microemulsions were investigated. The alpha-hydroxybenzyl radical generated from the hydrogen abstraction of the triplet state of BA from ethylene glycol (EG) or surfactant molecules was observed. The radical pair mechanism (RPM) and triplet mechanism (TM) and computer simulation were applied to express the photolysis. The intensity of CIDEP signals, the lifespan of the radicals and the polarization mechanism were different in EG, micelles or microemulsions because of their different micro structures. (C) 2002 Elsevier Science B.V. All rights reserved.