A new porous metal–organic framework (TMU-21) that is isostructural to our recently reported TMU-6 is introduced. The structure of this framework has been determined by X-ray crystallography and further characterized by Fourier transform infrared spectroscopy, elemental analysis, and thermogravimetric analysis. Its structural features as well as its stability and porosity were studied. These two metal–organic frameworks are interesting candidates for a comparative fluorescence study. Thus, their potential abilities to sense nitrobenzene, benzene, and polycyclic aromatic hydrocarbons, namely, naphthalene, anthracene, and pyrene, were investigated. This study clearly shows an important contribution of extending the π-electron systems of pillaring linkers in the ability of metal–organic frameworks to sense aromatic compounds.