The preparation of the flexible aniline-based covalent organic frameworks used for uptaking iodine and sensing picric acid and iodine

The flexible aniline-based conjugated microporous polymers with N-H and C-N bonds have excellent performances, but the flexible aniline-based covalent organic frameworks (COFs) have not been reported. In this paper, the flexible aniline-based COFs (TAPBDA and HAPBDA) were prepared by Schiff base reactions with flexible triazine-based aldehydes (TPT-3-CHO) and cyclophosphazene-based aldehydes (NOP-6-CHO), and flexible N1-(4-aminophenyl)benzene-1,4-diamine (APBDA) for the first time. They have 2D hexagonal and 3D triangular pores and flexible units which make the pores elastic and self-adaptable abilities. The resulting flexible aniline-based COFs exhibit high heat stability and some crystallization, and have fairly maximum adsorption capacities for I2 of 3.87 and 4.14 g g-1 with good recyclability. The flexible aniline-based COFs show good fluorescent properties both in solid and dispersion states and can be used for sensing picric acid (PA) with high quenching constants (KSV) of 2.82 x 104 and 1.66 x 104 L mol-1. Impressively, HAPBDA has excellent fluorescence sensing performance for iodine with KSV up to 9.98 x 104 L-1 mol.