Theoretical calculations on ions and radicals. II. SCFMO [self-consistent field molecular orbital] calculations on the excited states of aromatic nitriles and the spin density distributions of the corresponding anions

Intramolecular Radiative and Radiationless Charge Recombination Processes in Donor−Acceptor Carbazole Derivatives

“…In this correlation the values of E ox (D)− E red (A) are taken from the electrochemical data obtained for the given D−A molecule in ACN containing 0.1 M TBAPF 6 . These values, however, are very similar to those expected from the electrochemical properties of the donor and acceptor alone; the standard oxidation potentials E ox (D), as well as the standard reduction potentials E red (A), were close to the values found for CAR and a proper acceptor, respectively. The small shift of E red (A) to more negative potentials can be explained by the electron donating properties of 3,6-di- tert -butylcarbazole bonded to the acceptor subunit.…”

“…Following Dogonadze et al, the electronic coupling element V AD between the 1 CT state and the ground state can be related to the sum of the products of the LCAO coefficients of the highest occupied molecular orbital (HOMO) at an atom in the donor moiety and of the lowest unoccupied molecular orbital (LUMO) at another atom in the acceptor subunit and the corresponding resonance integrals β ad ( r ad , φ ad ) for the given pair of atoms By assuming that V AD is mainly determined by the interactions between the carbon and nitrogen atoms forming A−D bond (which is reasonable because the resonance integral β ad is an exponential function of a distance) and by neglecting contributions from the σ orbitals, the above relationship can be simplified where ϑ A - D is the angle between the planes of the donor and acceptor subunits and C LUMO and C HOMO are the corresponding LCAO coefficients of the 2p z atomic orbitals (where z is the axis perpendicular to the acceptor ring) of the carbon and nitrogen atoms forming A−D bond, respectively. The values C LUMO and C HOMO can be obtained in two independent ways: (i) from semiempirical AM1 calculations and (ii) from the hyperfine structure of the ESR spectra of the respective radical anions and cations . Both methods yield very similar values (Table ).…”