Knowledge Bank

Relative phosphorescence intensities and life times of two common iridium phthalocyanine aggregates in $\alpha -chloronapthalene$ between 5K and 80K were studied. From the data activation energies of intersystem crossing were obtained as follows: For crossing from the first excited singlet to the lowest triplet state $Ea=44\pm 10cm-1$ and $Ea=21\pm 5cm-1$ respectively; for crossing from the lowest triplet to the ground singlet state $Eap=42\pm 10cm-1$ and $Eap=29\pm 10cm-1$ respectively. These activation energies are several times as large as those reported for monomeric platinum phthalocyanine in the same solvent (1). A tentative explanation of this difference will be offered.