Figure 7. Calculated frontier molecular orbital energies (eV) of the nitrobenzene, toluene, and Zn-MOF.
These results are consistent with the quenching mechanism that has been widely accepted for this type of luminescence chemosensor for nitroaromatics compounds. According to literature, deactivation of the luminescent is produced by the transfer of electrons, after a photoinduced excitation, between the conduction band of MOF and lowest unoccupied molecular orbital of the analyte. 60-61Finally, the calculations of Zn-MOF-toluene system showed that the active molecular orbitals are similar to the Zn-MOF without a guest. It should also be noted that according to observed experimentally, in the presence of toluene, it is not observed fluorescence attenuation. The result also suggests that the mixture of the Zn-MOF orbitals and the analyte orbitals in the active space has an important role in the quenching of fluorescence.