Knowledge Bank

The incorporation of large molecules in n-alkane solid matrices$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ allows high resolution optical spectroscopy ($\Delta \nu =1$ $cm-1$) both in emission and absorption. Recent studies on tetrapyrrole dyes have also demonstrated a surprisingly high degree of orientation of the guest compound in the alkane lattice. The lowest excited triplet state of these compounds has been studied by the simultaneous application of microwaves and narrow band optical excitation in the absence of a magnetic field. Microwave absorption is monitored by recording molecular emission. Zero-field parameters and kinetic data on the separate magnetic sublevels of the triplet have been obtained for several tetrapyrrole complexes and can be related to their electronic structure and $symmetry.2$ Combining the Shpolskii media with optical selection by laser excitation opens new pathways for the study of compounds. of biological interest, which usually are not very attractive from a spectroscopic point of $view.3$