Low-lying π* resonance states of DNA and RNA bases have been investigated by the recently developed projected complex absorbing potential (CAP)/symmetry-adapted cluster-configuration interaction (SAC-CI) method using a smooth Voronoi potential as CAP. In spite of the challenging CAP applications to higher resonance states of molecules of this size, the present calculations reproduce resonance positions observed by electron transmission spectra (ETS) provided the anticipated deviations due to vibronic effects and limited basis sets are taken into account. Moreover, for the standard nucleobases, the calculated positions and widths qualitatively agree with those obtained in previous electron scattering calculations. For guanine, both keto and enol forms were examined, and the calculated values of the keto form agree clearly better with the experimental findings. In addition to these standard bases, three modified forms of cytosine, which serve as epigenetic or biomarkers, were investigated: formylcytosine, methylcytosine, and chlorocytosine. Last, a strong correlation between the computed positions and the observed ETS values is demonstrated, clearly suggesting that the present computational protocol should be useful for predicting the π* resonances of congeners of DNA and RNA bases.

The photophysical properties of oligosilanes show unique conformational dependence due to σ-electron delocalization. The excited states of the SAS, AAS, and AEA conformations of peralkylated n-hexasilanes, in which the SiSiSiSi dihedral angles are controlled into a syn (S), anti (A), or eclipsed (E) conformation, were investigated by using UV absorption, magnetic circular dichroism (MCD), and linear dichroism spectroscopy. Simultaneous Gaussian fitting of all three spectra identified a minimal set of transitions and the wavenumbers, oscillator strengths, and MCD B terms in all three compounds. The results compare well with those obtained by using the symmetry-adapted-cluster configuration interaction method and almost as well with those obtained by time-dependent density functional theory with the PBE0 functional. The conformational dependence of the transition energies and other properties of free-chain permethylated n-hexasilane, n-Si Me , was also examined as a function of dihedral angles, and the striking effects found were attributed to avoided crossings between configurations of σσ* and σπ* character.

Despite its industrial importance, very limited mechanistic information on the dehydrogenative coupling of dimethyl phthalate has been reported. Herein we report the detailed mechanism for dehydrogenative coupling of dimethyl phthalate catalyzed by [Pd­(OAc)2]/[Cu­(OAc)2]/1,10-phenanthroline·H2O (phen·H2O). The solution-phase analysis of the catalytic system by XANES shows the active species to be Pd­(II), and EXAFS supports the formation of an (acetato)­(dimethyl phthalyl)­(phen)­palladium­(II) complex from [Pd­(OAc)2]. A formation pathway of tetramethyl 3,3′,4,4′-biphenyltetracarboxylate via disproportionation of independently prepared [Pd­(OAc)­{C6H3(CO2Me)2-3,4}­(phen)] is observed with regeneration of [Pd­(OAc)2(phen)].