Fluorescent crystals and co-crystals of 1,8-naphthalimide derivatives: synthesis, structure determination and photophysical characterization

A series of 4-pyperidinyl-1,8-naphthalimide derivatives containing at the N-position an n-methylpyridine (n = 2, 3, or 4) have been synthesized and isolated as crystalline materials. These isomers were further reacted, in the solid state, with the co-former 1,4-diiodotetrafluorobenzene (I2F4) to give three new co-crystals of the general formula n<inf>2</inf>·I2F4. All crystalline materials have been thoroughly characterized in the solid state via single-crystal and powder X-ray diffraction, infrared spectroscopy and thermal methods; in addition, the photophysical properties of all compounds have been investigated in solution and in the solid state. The fluorescence features of the crystalline solids depend on the different arrangement of the molecules in the lattice and co-crystallization leads to important changes in the emission properties of the crystalline compounds. Emission quantum yields of the solids vary between 0.11 and 0.50.