Photophysical Properties of Phthalimide and Pyromellitic Diimide Tethered Imidazolium Nitrophenolate Salts

Abstract Structural aspects of the salt of 2‐(3‐(1H‐imidazol‐1‐yl)propyl)isoindoline‐1,3‐dione ( L 1 ) with 2,4,6‐trinitrophenol as well as the salts of N,N′‐bis(3‐imidazol‐1‐yl‐propyl)‐pyromelliticdiimide ( L 2 ) with 2,4‐dinitrophenol ( H24dnp) and 2,4,6‐trinitrophenol ( H246tnp) are reported along with the solid and solution studies on the photophysical properties of these salts. The fluorescence emission of the L 1 and L 2 are quenched by H24dnp and H246tnp both in solid and in solution. In solution the L 1 has comparable binding constant with H24dnp and H246tnp but the relative ability to quench the fluorescence emission of L 1 by H24dnp is less than the quenching abilities of the H246tnp . These two nitrophenols independently do not distinguish the L 1 from L 2 but the extent of quenching caused independently by the H24dnp or H246tnp on L 1 or L 2 make them easily distinguishable. Addition of water quenches the fluorescence emission of L 1 and L 2 ; but the addition of water to solution of the nitrophenolate salts result in the recovery of fluorescence emissions from the quenched states. The salts in solid state have short emission life‐times. The PET effect prominently caused by mineral acids on L 1 or L 2 is not observed in the nitrophenolate salts. In solid state the O‐π interactions contributed to stacking of the aromatic in the 2,4,6‐trinitrophenolate salt of L 2 , hence it is non‐fluorescent.