Knowledge Bank

The luminescence spectra, lifetimes, and quantum yields of platinum phthalocyanine (PtPc) in $\alpha$-chloronaphthalene ($\alpha$-C1N) were studied as a function of temperature (between $2\circ K$ and $300\circ K$) and sample preparation. At least two molecular species of PtPc (presumably differently sized aggregates) were identified. They differ in their phosphorescence spectra and lifetimes. The larger and/or chemisorbed aggregate was red-shifted vis-a-vis the smaller species and showed faster nonradiative decay. From our data we determined an activation energy of $16+2cm-1$ for the intersystem crossing. Activation energies of phosphorescence of the order of 10 $cm-1$ were also determined. This activation energy appeared to become smaller as the aggregate became larger or chemisorbed.