Theoretical investigation on excited state intramolecular proton transfer of 1-aryl-2-(furan-2-yl) butane-1, 3-diones substitutions

Abstract The effect of different substituents on the excited state intramolecular proton transfer (ESIPT) of 1-aryl-2-(furan-2-yl)butane-1,3-diones (AYFBD), namely OFBD, TFBD, MFBD and FFBD are studied by employing the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. By comparing the geometric configurations and infrared vibrational spectra of the first excited state (S 1 ) with those of the ground state (S 0 ), it can be concluded that the intramolecular hydrogen bonds are strengthened in S 1 state. The calculated peaks of absorption and fluorescence spectra of AYFBD derivatives in keto form are consistent with experimental results reported previously ( Journal of Organic Chemistry , 2017, 82 , 12097). We can also confirm that the intensities of the intramolecular hydrogen bonds in the S 1 state are enhanced by analyzing the frontier molecular orbitals and the infrared spectra. To further investigate the ESIPT mechanism of AYFBD derivatives, the potential energy curves (PECs) of S 0 and S 1 states are scanned by varying O 1 H 2 distance, which demonstrates that ESIPT occurs in the S 1 state of all the AYFBD derivatives and follows the order: FFBD > MFBD > TFBD > OFBD.