Prolonging luminescent lifetimes by introducing bis(maleonitriledithiolato)metalate anions with a fluorescent organic cation

Abstract

A new organic fluorescent ionic compound [MOBIP]I (1) (MOBIP⁺= 1-methyl-2-oxo-3 -(1H-benzimidazol-2(3H)-ylidene)-2,3-dihydropyridinium) was synthesized and used to prepare seven maleonitriledithiolate metal complexes [MOBIP] _n [M(mnt)₂] by substitution of the iodide ion with [M(mnt)₂] ^{n −} (M = Cu²⁺ (2), Ni²⁺ (3a), Ni³⁺ (3b), Zn²⁺ (4), Cd²⁺ (5), Pd²⁺ (6), and Pt²⁺ (7)). An investigation of fluorescence properties shows that these complexes are a new series of solution luminescent complexes of maleonitriledithiolate derivatives with strong blue light fluorescence in daylight by irradiation with UV light with high quantum yields. They display similar symmetric emissions with λ_em at the deep blue region of ∼426 nm upon excitation at ∼364 nm in DMF, caused by L–L transition of MOBIP⁺. Existence of [M(mnt)₂] ^{n −} anions in the solution prolongs the fluorescent lifetimes. For all these compounds in the solid state, the fluorescent emission is blue-shifted and more narrow than that in solution. Based on their crystal structure analysis, the weak stacking interactions in compounds cause the difference of their fluorescence spectrum. Investigations of variable-temperature magnetic susceptibility indicate that 2 has weak antiferromagnetic coupling, while 3b exhibits stronger antiferromagnetic coupling.

Keywords:

• Bis(maleonitriledithiolato)metalate anion
• Fluorescent properties
• Crystal structure
• Magnetic properties

Acknowledgments

This work was supported by the National Basic Research program of China (2007CB925102), the National Natural Science Foundation of China (NSFC: 20771056), the State Basic Research Project of China (NSFC: 20490218), and the Center of Analysis and Determining of Nanjing University.