Die langwellige Fluoreszenz des Pyren-3-aldehyds / The long wave fluorescence of pyrene-3-aldehyde

On concentrating liquid solutions of pyrene-3-aldehyde a fluorescence of long wave length appears with increasing intensity. It reminds of the excimer fluorescence of pyrene but behaves differently in some respects.

It shows a distinct dependence on solvent and excitation wave length: Whereas it may be observed with high intensity in an unpolar solvent such as n-heptane, it is completely suppressed in the strongly polar acetic acid. When it is excited in the weak long wave length part of the first absorption band, the quantum yield is higher than with excitation at shorter wave lengths.

In hydrogen free liquid solvents the fluorescence also could be detected as a delayed emission.

It is assumed that weakly bound dimers are present already in the ground state of the aldehyde, these being directly excited to the excimer state.