The fluorescence properties of crystalline anthracenes and their dependence on the crystal structures

The fluorescence properties of a number of crystalline anthracenes are described. It is found that in excimer‐emitting crystals the energy of the emission is shifted by change in temperature much more strongly in infinite‐stack structures than in structures based on pair‐wise packing. A theoretical treatment is given of the general problem of the excimer emission from a crystal, and is applied to the anthracenes. This theory shows that the sensitivity to temperature for high temperatures is determined by the ratio of the frequencies of intra‐pair vibrations in ground and excited states of the particular material. An interpretation of the difference in this ratio for stack and pair structures is given, and some predictions based on this interpretation are given and tested. It is confirmed that structures in which molecular overlap is small give rise to monomer emission.