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Spectroscopic and DFT studies of donor–acceptor molecules containing phenylquinoline and phenothiazine moieties in various redox states
Author(s) -
Ponce Ortiz R.,
Malavé Osuna R.,
Ruiz Delgado M. C.,
Casado J.,
Jenekhe S. A.,
Hernandez V.,
Lopez Navarrete J. T.
Publication year - 2005
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.20521
Subject(s) - chemistry , phenothiazine , homo/lumo , delocalized electron , molecular orbital , photochemistry , molecule , density functional theory , radical ion , electron acceptor , computational chemistry , ion , organic chemistry , medicine , pharmacology
Abstract We report the ultraviolet (UV)‐Vis, Fourier transform‐infrared (FT‐IR), and FT‐Raman spectroscopic study of an electrogenerated chemiluminescence (ECL) emitting compound containing two electron‐accepting phenylquinoline end groups covalently attached to an electron‐donating 10‐methylphenothiazine central moiety. The optimized molecular geometry of the neutral compound as determined from quantum chemical density functional theory (DFT)//B3LYP/3‐21G* calculations shows that the phenyl groups appended onto the quinolines are twisted by ≈62° from these moieties. The sulfur atom is also tilted with respect to the plane defined by the phenyl rings of the phenothiazine, in both the neutral and singly oxidized species. The highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of the neutral systems partially overlap, so that the lowest‐energy visible absorption band implies a certain degree of charge transfer from the phenothiazine toward the phenylquinolines. In contrast, the removal of the first electron mainly affects the structure and equilibrium charge distribution of the phenothiazine, and much less in those of the quinolines. In addition, the DFT//UB3LYP/3‐21G* topologies of the molecular orbitals around the bandgap region of the radical cation reveal no molecular orbital overlap between the two types of constituent building blocks, thus inhibiting the delocalization of the injected positive charge over the whole molecule. This feature could be in line with the ability of this system to generate localized radical ions capable of displaying chemiluminescence upon annihilation, as previously observed experimentally. The UV‐Vis and FT‐Raman spectra of the singly oxidized species generated upon treatment with FeCl 3 in CH 2 Cl 2 solution have also been recorded. The experimental data were interpreted with the help of DFT calculations. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005