Molecular Fluorescence from High Vibrational Levels of Excited Electronic States

Contrary to common belief, fluorescence from high vibrational levels of the lowest excited electronic singlet state of certain complex molecules in liquid and solid solution is observable and can be a valuable spectroscopic tool for the study of intramolecular energy-transfer processes. Several such fluorescent levels were identified in magnesium phthalocyanine in $\alpha$-chloronaphthalene with quantum efficiencies of the order of ${10}^{-3\mathrm{}}$ at 77°K and ${10}^{-4\mathrm{}}$ at 300°K in the visible spectral region.