A DFT/TDDFT study on spectral effects of metal ion interactions with benzofurazan-based fluorescent probes

CAM-B3LYP DFT/TDDFT calculations have been performed on two fluorescent benzofurazan derivatives and their complexes with metal ions ($Zn^{2+}, Na^{+}, K^{+}, Mg^{2+}$ and $Ca^{2+}$). Optimized structures of complexes and binding energies have been determined. Calculated vertical transition energies have been compared to available experimental data. Only one ligand binds effectively $Zn^{2+}$ ion allowing metal orbitals to par- ticipate in frontier molecular orbitals which results in significant shifts in absorption and emission spec- tra. Modified structure of the other ligand makes ion binding less effective. It has been shown that proper reproduction of transition energies requires accounting for state-specific solvation.