The Electronically Excited-State of the MFU-4 [Zn5Cl4(BBTA)3] Metal-Organic Frameworks: Time-Dependent Density Functional Theory Study

The density functional theory (DFT) and time-dependent density functional theory (TDDFT) have been carried out to investigate luminescent property of [Zn5Cl4(BBTA)(3)]. The frontier molecular orbitals and electronic configuration of the MOF [Zn5Cl4(BBTA)(3)] have been calculated using DFT. The results shown that the luminescent mechanism in the nature of the [Zn5Cl4(BBTA)(3)] should be the ligand-to-ligand charge transfer (LL'CT) and the transition from HOMO to LUMO be delocalized excitation. The geometric structures of the electronically excited state of the [Zn5Cl4(BBTA)(3)] was optimized using the TDDFT method. The Zn1-N1 and Zn2-N2 coordination bonds were strengthened in the electronically excited state which is confirmed by the bond length, bond order and the stretching vibration frequency of the Zn1-N1 and Zn2-N2 bonds. Combined with luminescent mechanism, we further explained that the Zn1-N1 and Zn2-N2 bonds strengthening in the electronically excited state can promote the luminescent of the [Zn5Cl4(BBTA)(3)].