Abstract

Photoinduced charge separation reactions in a large series of rigid porphyrin-triptycene-quinone (donor-spacer-acceptor) molecules were studied with picosecond transient absorbance and fluorescence techniques in polar and non-polar solvent at room temperature and at 77K in MTHF glass. At 77k the fluorescence yield as a function of free energy sharply inflects at 0.6eV. However at room temperature in toluene a less pronounced inflection occurs at 0.3eV. These inflection points represent the driving force where the rates of electron transfer approach the fluorescence decay rate of the porphyrin. Only when the energy of the ion pair state is lower than the lowest excited singlet state of the porphyrin may electron transfer occur.

© 1990 Optical Society of America