Crystal excimer fluorescence from substituted naphthalenes

Excimer emission is observed from thermodynamically stable, ordered crystals of two napthalene derivatives, namely 1,3-dichloronaphthalene and 1,4-dichloronaphthalene. At 77 K 1,3-dichloronaphthalene has a fluorescence maximum at 398 nm, a decay time of 14 ns and a quantum yield of 0.13. The corresponding values for the 1,4-derivative are 400 nm, 11 ns and 0.10. Crystals of both compounds are photostable upon UV irradiation at room temperature.