UV-visible absorption spectra
The UV-visible absorption spectra of AB1 and AB2 are plotted in Figure 5 and the calculated maximum peak of the UV-visible absorption (λabs), excitation energy (E), oscillation strength (f ), of the compounds AB1 and AB2 are summarized in Table 6. The peaks of the absorption spectra of theAB2 (λabs = 312 nm) is red-shifted compared with the moleculeAB1 (λabs = 287 nm). It can be said that the introduced NO2 groups has greatly affected the absorption spectra due to the increased intermolecular interactions in solid phase. The electronic excitations of both compounds are controlled by the transition from HOMO to LUMO.