Spectroscopy and Photophysics of Monoazaphenanthrenes III. Luminescence of Phenanthridine and 7,8-benzoquinoline in Crystalline State

M. Norek, B. Kozankiewicz and J. Prochorow Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland

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Received: April 3, 2004

Fluorescence and phosphorescence spectra and the decay profiles of both these emissions have been investigated for the polycrystals of phenanthridine and 7,8-benzoquinoline, in the liquid helium (5 K) - room temperature range. These two monoazaderivatives of phenanthrene, which differ only by the position of N-heteroatom in the aromatic ring skeleton of phenanthrene, were found to exhibit very different fluorescence spectra, which also differ greatly in their temperature behavior. Supplementary investigations of the fluorescence of single crystals of 7,8-benzoquinoline have supported classification of observed fluorescence as an excimer fluorescence (caused by the specific arrangement of molecules of 7,8-benzoquinoline in the crystal). In contrary fluorescence of phenanthridine crystals is of the monomeric type. Phosphorescence spectra observed for the crystals of both molecules are very similar, but their temperature dependence is also different. This may be considered as an indication of a different physical mechanism of nonradiative intersystem crossing processes, which are operating between the lowest excited singlet state and the lowest excited triplet state in the crystals of both molecules.

DOI: 10.12693/APhysPolA.106.77 PACS numbers: 78.55.Kz, 33.50.Dq