PHOTO-CHEMICAL ELECTRON-TRANSFER IN MONOLAYER ASSEMBLIES .1. SPECTROSCOPIC STUDY OF RADICALS PRODUCED IN CHLOROPHYLL-A-ACCEPTOR SYSTEMS

Chlorophyll monolayers together with an acceptor species such as sublimed chloranil cause a light-induced electron paramagnetic resonance (EPR) signal. Under steady-state illumination, the rise and decay of this signal were of the order of minutes. Under flash illumination, the decay time of this signal was 0.6 ms and was temperature independent. An experiment using deuterated chlorophyll monolayers with bromanil resulted in a narrow light-induced signal with a g factor of 2.0025 and a broad signal with a g factor near 2.009. These signals were attributed to the chlorophyll radical cation and the bromanil anion, respectively. In a separate experiment we generated the chlorophyll radical cation in monolayers using iodine vapor. The resulting EPR signal had a g factor of 2.0025 and the life width indicated that the signal was due to monomeric chlorophyll species. We also measured the magnetic circular dichroism (MCD) spectrum of monolayer assemblies of chlorophyll with surface-active acceptor species. We found light-induced bleaching at 680 nm with enhancement occurring at 660 and 672 nm. © 1979, American Chemical Society. All rights reserved.