Insights into the excited state dynamical process for 3-hydroxy-2-(5-(5-(5-(3-hydroxy-4-oxo-4H-chromen-2-yl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)-4H-chromen-4-one

In this present work, we theoretically investigate a novel system 3-hydroxy-2-(5-(5-(5-(3-hydroxy-4-oxo-4H-chromen-2-yl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)-4H-chromen-4-one (FT) based on density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Via calculating the reduced density gradient (RDG) versus sign(lambda(2)) rho, we firstly verify the formation of the dual intramolecular hydrogen bonds (O1H2 center dot center dot center dot O3 and O4H5 center dot center dot center dot O6) for FT form in the S-0 state. Then comparing the primary structural parameters and corresponding infrared (IR) vibrational spectra involved in hydrogen bonds between S-0 and S-1 state, we demonstrate that these two intramolecular hydrogen bonds should be strengthened in the S-1 state. Insights into the vertical excitation process, our theoretical results reproduced experimental absorption nature, which confirms that the theoretical level (B3LYP/TZVP) is reasonable and effective in this work. And frontier molecular orbitals (MOs) depict the nature of electronically excited state and support the excited-state intramolecular proton transfer (ESIPT) reaction. According to the calculated results of potential energy curves along stepwise and synergetic O1H2 and O4H5 coordinates, we verify that only the excited-state single-proton transfer could occur for FT molecule in the S-1 state, although it possesses two intramolecular hydrogen bonds. We not only investigate the detail excited-state behaviors for FT system and elaborate the ESIPT mechanism but also explain previous experimental results.