The effect of furcated hydrogen bond and coordination bond on luminescent behavior of metal-organic framework [CuCN·EIN]: A TDDFT study

The hydrogen bonding in electronically excited-state of the metal-organic framework [CuCN·EIN] was studied using time-dependent density functional theory (TDDFT). The representative fragment of [CuCN·EIN] was employed for the computation. The geometric structures, binding energies and IR spectra in both ground state and electronically excited state S1 of the complex were computed using DFT and TDDFT methods to investigate excited-state hydrogen-bonding and coordination bonding, respectively. Based on the analysis of the frontier molecular orbitals and the electronic configuration of the complex, the ligand-to-metal charge transfer (LMCT) luminescence was confirmed. Furthermore, furcated hydrogen bonds are both strengthened in the S1 state slightly. And then, the strengthening of the hydrogen bonds in the S1 state goes against the charge transfer from ligand to metal and then should be in favor of the luminescence. In particular, we also discuss strengthening or weakening behavior of the coordination bonds in the S1 state for the first time. Based on the results of the bond lengths and vibration frequency of the coordination bond, we can conclude that the coordination bond Cu7–N8 is strengthened in the S1 state. And the strengthening of the coordination bond Cu7–N8 should also be in favor of the luminescence.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The effect of furcated hydrogen bond on luminescent behavior is studied. ► TDDFT is used to study the excited-state hydrogen bonding. ► The effect of coordination bond on luminescent behavior is studied. ► Luminescence can be caused by the ligand-to-metal charge transfer (LMCT) form.