Polyhalogenated aminobenzonitrilesvs.their co-crystals with 18-crown-6: amino group position as a tool to control crystal packing and solid-state fluorescence

Strengthening ( para -isomers) or weakening ( ortho -isomers) of π-electron aggregation due to the crystal structure rearrangement results in the bathochromic or hypsochromic shift of the fluorescence maximum.