This work reports on a monomer-dimer equilibrium state of pheophorbide a in
solution. A methodology for controlling the equilibrium constant by use of
temperature and solvent variation is described. The absorption spectrum of
the dimer is calculated, using different prepared equilibria of monomer an
d dimer in solution. We propose that these aggregates provide a good model
for understanding the dimerization process in tetrapyrroles. (C) 2000 Elsev
ier Science S.A. All rights reserved.