A computational study on the relative reactivity of reductively activated 1,4-benzoquinone and its isoelectronic analogs

Long-range ordered nanodomains of grafted electroactive molecules

We demonstrate the capability to build zero and one-dimensional electroactive molecular nanostructures ordered over a macroscopic scale and stable under ambient conditions. To realize these arrays, we use the selective grafting of functionalized thiols (juglon and terthiophene based) on a self-organized metallic template. The nanoscale patterning of the molecular conductance is demonstrated and analyzed by scanning tunneling spectroscopy. Finally, the influence of the nanostructuring on electro-chemical properties is measured, paving the way to an all-bottom-up fabrication of nanostructured templates for nanosciences.

Electron affinities of p-benzoquinone, p-benzoquinone imine and p-benzoquinone diimine, and spin densities of their p-benzosemiquinones computed by several quantum chemical models

Restricted and unrestricted (U) Hartree-Fock (HF), second-order Møller-Plesset perturbation (MP2), density functional (DF), hybrid HF/DF and semiempirical (half-electron (HE) method) models have been used to calculate adiabatic electron affinities (EAad values) of p-benzoquinone (I), p-benzoquinone imine (VI) and p-benzoquinone diimine (XI), as well as expectation values (<S2>) and spin density distributions in the radical anions of I, VI and XI. The AM1/AM1-HE and ab initio calculated structures are found to be in accord with each other. The ROHF/6-31G(d) method gave the poorest EAad result. The UHF and UMP2 wave functions were found to be substantially spin contaminated (for the radicals) and the accuracies of the EAad values calculated were also poor. The use of molecular energies obtained after spin annihilation did not lead to significant improvement of the UHF and UMP2 results. In contrast to the ROHF, UHF and UMP2 results, the DF(USVWN, UBVWN, UBLYP) and hybrid HF/DF(UB3LYP) methods, as well as the AM1-HE, gave much better results. The calculated EAad values decreased, as predicted by most of the models, in the order EAad(I) > EAad(VI) > EAad(XI). The differences in the EAs, EAad(I)-EAad(VI) and EAad(I)-EAad(XI), were consistently predicted to be about 8-9 and 17-18 kcal/mol, respectively, by the DF, B3LYP and AM1-HE models. The performance of the PM3 and SAM1 models was not as good as the AM1 model. Of all the methods tested, the B3LYP/6-311G(d,p) model is concluded to give the most accurate quantitative trend (I(42.6) > VI(33.1) > XI(23.7)) in EAad. The predicted trend in EA can satisfactorily be rationalized by the calculated LUMO orbital energies, atomic charges and spin density distributions. Analysis of the spin density data predicts that phenoxyl- and anilino-type radical anions predominate in the p-benzosemiquinones of I and XI, respectively, while both phenoxyl- and anilino-type radicals contribute to the structure of the p-benzosemiquinone of VI, with the anilino-type predominating.