Based on the characteristics of a nitro-group, which can be partially or totally reduced to an amino-group in hypoxic cells, two series of hypoxic sensors containing 7H-Benzimidazole [2,1-a]benz[de]isoquinolin-7-one cores with nitro groups in different positions were designed, synthesized and evaluated. The target compounds exhibited significantly different fluorescence characteristics (fluorescence enhancement or quenching). The strong fluorescences of some partially reduced compounds could be explained through the examination of their infrared spectra, which showed a restriction of the nitro-group vibration. These compounds exhibited significant hypoxic-oxic fluorescence differences not only in numerical values but also in their fluorescent imaging properties as reported for the first time.