Phosphorescence and Fluorescence of Phthalocyanines

For the first time, phosphorescence has been observed from and clearly assigned to the molecular triplet of several metallophthalocyanine (Pc) molecules. The Pc's of Pt, Pd, Cu, Zn, and Cd have $\mathrm{O}–\mathrm{O}$ bands in solution (77°K) at the extraordinarily low energies of 10 590, 10 100, 9390, 9150, and $\text{9120\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ , respectively, while those of Mg and VO have possible transitions at $\text{∼9000}$ and $\text{8500–8800\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ . Half‐widths, lifetimes, approximate quantum efficiencies, triplet absorption, and excitation spectra, and vibrational substructure are reported, together with oxygenation and heavy atom effects. The lifetimes were very short (varying from 1 msec to less than 3 μsec), so room temperature phosphorescence was seen, as was radiation from the separate triplet sublevels at 4°K and below. Yields were very low (${\text{∼10}}^{\text{−2}}$ to ${\text{∼10}}^{\text{−5}}$ ) because of very strong radiationless transitions, and various other Pc complexes did not seem to phosphoresce at all. Both tripdoublet and quartet luminescence were seen from CuPc, and the intersystem crossing time was estimated to be $\text{∼1}$ nsec. Fluorescence is reported from several of the complexes, including PdPc.