Synthesis, physical properties, and sensing behaviour of a novel naphthalenediimide derivative

•A novel naphthalenediimide derivative 4NHNDI was obtained as an unexpected byproduct.•The possible mechanism was discussed.•4NHNDI can emit strong red light and act as an efficient sensor for fluoride ion.

In our attempt to prepare compound 4,5,9,10-tetraamino-2,7-bis(2-octyldodecyl)benzo[lmn] [3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (4NH2NDI) according to the reported procedure for constructing larger conjugated molecules, an unexpected by-product 2,8-bis(2-octyldodecyl)-5,5,11,11-tetraphenyl-5,6,11,12-tetrahydroimidazo[4′,5′:5,6]benzo[1,2,3,4-lmn]imidazo[4,5-f] [3,8]phenanthroline-1,3,7,9(2H,4H,8H,10H)-tetraone (4NHNDI) was obtained through the undesired hydrolysis of 4,5,9,10-tetrakis((diphenylmethylene)amino)-2,7-bis(2-octyldodecyl)benzo[lmn] [3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (4NNDI) when a drop of water was added in this reaction. The undesired hydrolysis was furthered confirmed by the direct hydrolysis of pure 4NNDI in organic solvent with a drop of aqueous HCl solution.4NHNDI was fully characterized by NMR and mass spectroscopy and was further confirmed through a single crystal analysis. The absorption and emission wavelengths of 4NHNDI were red-shifted ～ 20 and 30 nm with the increased polar of the solvents due to the dipole–dipole interactions between 4NHNDI and the polarity solvents. Interestingly, 4NHNDI can act as an efficient anion sensor for fluoride ion over a wide range of other anions (ClO4−, Br−, BF4−, I−, NO3−, Cl−, PF6−, AcO−, HSO4- and CN−) owing to the four NH fragments in the main backbone. Surprisingly, 4NHNDI didn't show any sensing behavior in aqueous solutions to all eleven anions including F- anion, which might be due to the steric effects from long alkyl chains in aqueous solution. However, this phenomenon could allow us to recover the quenched spectrum induced by F− anion through adding H2O in pure THF solution.

Graphical abstractA tetrahydroimidazo core-substituted NDI derivative 4NHNDI was successfully synthesized and it can act as an efficient anion sensor for fluoride ion over a wide range of other anions.Figure optionsDownload full-size imageDownload as PowerPoint slide