ABSTRACT
Coupling rates between the radicals methyl, n-, sec-, tert-butyl and benzyl (R.) and the aromatic radical anions of 1,4-dicyanonaphthalene, 9,10-dicyanoanthracene and fluorenone (A-.) have been obtained using a new laser-flash photolysis method. The radicals R. and the radical anions A-. were generated by a photoinduced electron transfer reaction between the aromatic compound A and the alkyl or benzyl triphenylborate anion RB(Ph)3-. For the first time the rate constants of the coupling reaction between methyl and benzyl radicals with aromatic radical anions have been obtained. For all the measured coupling rate constants an average value of k1 = 1.9 x 10(9) M-1 s-1 was found with a relatively small variation in the coupling rates (0.8-2.9 x 10(9) M-1 s-1). The results demonstrate that the coupling rate k1 is insensitive to changes in the steric and electronic properties of the radicals and the structure and standard potentials of the aromatic radical anions.
ABSTRACT
The radical cation of 1,3,6,8-tetraazatricyclo [4.4.1.1(3,8)]dodecane (TTD) has been studied using magnetic resonance and optical spectroscopic methods and computational techniques. With the help of deuterated isotopomers, assignments of EPR and resonance Raman spectra could be unequivocally established. The results demonstrate that the radical cation has D(2d) symmetry, and instantaneous electron delocalization over the four equivalent nitrogen atoms occurs. This extensive delocalization in a completely saturated system is a unique feature of the TTD radical cation. The spectroscopy of TTD, in contrast to that of simpler diamines such as 1,4-diaza[2.2.2]bicyclooctane, simultaneously reveals the consequences of orbital interactions through space and through bonds. The relationship between nitrogen pyramidalization and hyperfine coupling constants in nitrogen-centered radical cations with a number of different bonding arrangements is reviewed.
ABSTRACT
Trioxatriangulenium (TOTA+. 4,8,12-trioxa-4,8,12,12c-tetrahydro-dibenzo[cd,mn]-pyrenylium) is a closed shell carbenium ion, which is stable in non-nucleophilic polar solvents at ambient temperatures In alcohols, small quantities of the leuco ether are formed in a reversible reaction. The physical and chemical properties of the excited singlet state of the trioxatriangulenium (TOTA+) carbenium ion are investigated by experimental and computational means The degeneracy of the lowest excited states is counteracted by Jahn-Teller-type distortion, which leads to vibronic broadening of the long wavelength absorption band. A strong fluorescence is observed at 520 nm (tau(fl) = 14.6 ns, phi(fl) = 0.12 in deaerated acetonitrile). The fluorescence is quenched by 10 aromatic electron donors predominantly via a dynamic charge transfer mechanism, but ground state complexation is shown to contribute in varying degrees Quenching is also observed in the presence of halide ions Quenching rate constants are derived from lifetime measurements while charge transfer (CT) complex formation constants follow from the steady-state Stern-Volmer plots. CT-complex formation with three discogenic triphenylenes is studied separately. Phosphorescence spectra, triplet lifetimes. and triplet-triplet absorption spectra are provided. In the discussion, TOTA+ is compared to the unsubstituted xanthenium ion and its 9-phenyl derivative with respect to the excited state properties.
