Photo-physical properties of bromo-indolylmaleimide (IM-Br), indole-succinimide (IS), and their anions were theoretically investigated compared with the previous theoretical result for indolylmaleimide (IM) [Phys. Chem. Chem. Phys., 2010, 12, 9783]. The energies for the electronic excited states as well as the ground states were computed for these molecules using the multi-reference perturbation calculations based on the second order Rayleigh-Schrödinger perturbation theory (CASPT2) at the cc-pVDZ basis set level. The electron-accepting or electron-donating effect caused by bromine-substitution was discussed in the intra-molecular charge transfer (ICT) mechanism. The order of natural orbitals of the bromine-substituted monovalent anion with a deprotonated indole NH group (I (-)M-Br) was found to be rearranged by the effect of electron-donation, which leads to pseudo-crossing of the potential energy cures of the S 1 and S 2 states. The large stokes shift observed for I (-)M-Br was due to pseudo-crossing. Meanwhile, IM and IM-Br show abnormal deprotonation, which is explained by the charge distribution on the indole and maleimide moieties. Finally, the monovalent anions I (-)M-Br and I (-)M by a deprotonation of the indole NH end and the neutral IS were proposed to be the most feasible candidates corresponding to the experimental spectra in solution.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry