Intermolecular hydrogen bond and twisted intramolecular charge transfer in excited state of fast violet B (FVB) in methanol solution

• The twisted intramolecular charge transfer of FVB is investigated by TDDFT method.
• The hydrogen bonding strengthening in the excited state is demonstrated.
• The mechanism of TICT is clarified.

The excited state hydrogen bonding dynamics and corresponding photophysical processes of fast violet B (FVB) in hydrogen-donating methanol (MeOH) solution are investigated by using time-dependent density functional theory (TDDFT) method. In the FVB molecule, there are CO, NH groups which could act as hydrogen acceptor and donor. It is demonstrated that both the intramolecular hydrogen bond O⋯HN in FVB and intermolecular hydrogen bond CO⋯HO between FVB and MeOH are formed in the ground state S0 and strengthened in the excited state S1. The absorption spectra are obviously red shifted for the hydrogen-bonded complex in comparison with FVB monomer in the low energy range. The theoretical investigation demonstrates that the twisted intramolecular charge transfer takes place in the excited states for both isolated FVB and hydrogen-bonded complex, and the dominant twisting is along N2C3 bond. The potential energy curve is investigated to understand the photophysics process of FVB and hydrogen-bonded complex.

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