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 N-H 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. © 2016 Published by Elsevier Ltd.