Zinc tetraphenylporphyrin forms J-aggregates, consisting mainly of dimers at moderate concentrations, in freshly-prepared dry acetonitrile solution at room temperature. The kinetics of disaggregation of these dimers may be followed by monitoring their absorption and emission spectra and their fluorescence lifetimes as a function of time and temperature following dilution. The activation energy of the disaggregation process is 20.0 kJ mol(-1). (C) 2003 Elsevier Science B.V. All rights reserved.