Aramid-film pH sensitive fluorescence enhancement based on benzimidazole intermolecular hydrogen bonds.

The aramid-film containing benzimidazole units was synthesized, and its pH sensitive fluorescence enhancement effect was investigated. After surface-treated by acidic ethanol solution (pH 1), the aramid film exhibits noticeable emissive enhancement as high as 33 times than the blank sample. The fluorescence lifetimes of aramid films increase significantly from 0.9 × 10−10 s to 8.2 × 10−10 s. The driving force is ascribed to the decrease of nonradiative transition probability, which comes from the strengthening molecular rigidity of phenyl benzimidazole chromophore within the polymer chains, induced by hydrogen bonds between N-H in benzimidazole group and C=O in amide group. The hydrogen-bond effect is thoroughly proved through examining the repeating molecular units of the aramid polymer chains by the methods of XRD, UV–vis, photoluminescence, molecular simulation, SEM and etc. This pH sensitive fluorescence change should have great potential in the sensor-device design of NH 3 , heavy metal ions or other systems due to the subsequent fluorescence quench effect, because of the excellent mechanical and processability of aramid polymers. Due to the intensified molecular interaction caused by intermolecular hydrogen bonds, benzimidazole based aramid film is pH sensitive in fluorescence enhancement, which is a new finding with great potential in the sensor- or electronic device design of NH 3 , heavy metal ions or other systems based on the subsequent fluorescence quench effect for benzimidazole aramid PBIA film. [Display omitted] • Benzimidazole based aramid film is pH sensitive and fluorescence enhanced 33 times higher after HCl acid-ethanol treatment. • The fluorescence increase is caused by hydrogen bonds induced molecular interaction and radiative transition probability. • The hydrogen bonds are located between N-H in benzimidazole group and C=O in amide group of the chromophore. • This pH sensitive film should have great potential in sensors or electronics with the subsequent fluorescence quench. [ABSTRACT FROM AUTHOR]