Figure 2. Molecular orbital energy diagram for Zn-MOF showing
the vertical electronic transitions for the maxima absorption band at
B3LYP/def2-TZVPP theoretical level.
In order to carry out a strong analysis of host-guest interactions, the
Zn-MOF ground state was optimized with the incorporation of the
analytes. The analytes were selected considering the reported largest
and the lowest quenching efficiency of the Zn-MOF fluorescence;i.e. nitrobenzene (quenching, 84%) and toluene (non-quenching).31 All Zn-MOF-analyte systems were optimized at the
same theoretical level as the free Zn-MOF. The proposed input geometries
consisted on the pi-staking/aromatic interaction between the linkers and
target molecules. Two interaction models were considered for each
analyte, one where the interaction occurs with the aromatic ring of the
OBA linker while the other displays the interaction with the BPY
fragment. Both initial structures converged to the host-guest
interaction between the analyte and BPY, with a distance between them
within the range of 3.15–3.34 Å. Zn-MOF-nitrobenzene and Zn-MOF-toluene
minima structures were selected for the calculations and the analyzes
described below. The geometrical parameters computed for the Zn-MOF
interacting with the analytes did not show significant differences in
relation to the ground state of the free Zn-MOF, see Table S1,
Supporting Information.