Theoretical exploration about excited state proton transfer mechanism for a series of phenol–quinoline compounds

Abstract

In the present work, three novel phenols (10a,11‐dihydro‐4bH‐indeno[1,2‐b]quinolin‐4‐ol (1), 5,6‐dihydro‐benzo[c]acridin‐1‐ol (2), and 5,5,7,7a‐tetrahydro‐4aH‐13‐aza‐benzo[3,4]cyclohepta[1,2‐b]naphthalene‐1‐ol (3)) have been explored theoretically in detail. Using density functional theory (DFT) and time‐dependent DFT (TDDFT) methods, we inquire into the intramolecular hydrogen‐bonding interactions and the excited‐state intramolecular proton transfer (ESIPT) process. Exploring the steady‐state absorption and emission spectra under TDDFT/B3LYP/TZVP theoretical level in acetonitrile solvent, our calculated results demonstrate an experimental phenomenon. Based on analysis of the variations of geometrical parameters and infrared (IR) vibrational spectra, we confirm that O–H⋯N should be strengthened in the S1 state. Investigating the frontier molecular orbitals (MOs) and the charge density difference (CDD) maps, it can be confirmed that the charge redistribution facilitates the tendency of the ESIPT process for 1, 2, and 3 systems. By constructing potential energy curves, we confirm that the proton transfer should occur in the S1 state. In particular, the ESIPT for 2 and 3 systems are nonbarrier processes in the S1 state, which confirms that ESIPT should be exothermal spontaneously. This work explains previous experimental results and makes a reasonable assumption about the ESIPT mechanism for 1, 2 and 3 systems. We sincerely hope our work can facilitate understanding and promoting applications about them in future.

Tuning ESIPT-coupled luminescence by expanding π-conjugation of a proton acceptor moiety in ESIPT-capable zinc(ii) complexes with 1-hydroxy-1H-imidazole-based ligands

“…However, the quinoline moiety is only rarely involved in the design and theoretical studies of ESIPT-capable molecules. [139][140][141][142][143][144][145][146][147][148][149][150][151][152][153][154][155][156] What is important for coordination chemistry in the case of HL q is that this new ESIPT-system still features a metal binding site and can be used for the synthesis of ESIPT-capable metal complexes as its predecessor HL p is. Finally, since ESIPT-fluorophores tend to luminesce with low quantum yields resulting from significant structural reorganization accompanying the ESIPT process, a natural choice for improving their efficiency through chelation-enhanced fluorescence (CHEF) seems to be Zn 2+ ion.…”