Frederick Sanger's early work on protein sequencing through the use of colorimetric labeling combined with liquid chromatography involves an important nucleophilic aromatic substitution (S N Ar) reaction in which the N-terminus of a protein is tagged with Sanger's reagent. Understanding the inherent differences between this S N Ar reaction and other nucleophilic substitution reactions (S N 1 and S N 2) can be challenging for students learning organic chemistry. Here, both electrostatic potential (ESP) maps and natural bond orbital (NBO) analyses are employed to visualize and conceptualize Sanger's key observation of the difference in reactivity between 2,4-dinitrochlorobenzene and 2,4-dinitrofluorobenzene. The utility of this method is extended to compare the reactivity of a series of halobenzenes for S N Ar fluorination, a widely used reaction in pharmaceutical and medicinal fields. In combination with experimental results from the literature, the ESP maps and NBO analyses are consistent with and provide excellent corroboration with the reactivity of different substrates toward S N Ar reactions.

Photoinduced generation of excitons and their nonradiative relaxation dynamics are simulated at the interface of (10, 0) carbon nanotubes (CNT) and a PbSe nanowire (NW). Possible pathways of photoinduced excitations are explored by combining a reduced density matrix approach in the basis of Kohn–Sham orbitals and on-the-fly nonadiabatic couplings. A range of neutral photoexcitations localized on the CNT is followed by formation of charge transfer (CT) states involving PbSe NW. Depending on the wavelength of the incident light, the initial photoexcitation can be followed by two directions of charge transfer: either (PbSe)+(CNT)− or (PbSe)−(CNT)+. Excitation of a hot electron results in the CT state with an electron located at the NW and the hole at the CNT with shorter lifetime, while excitation of a hot hole leads to the CT state with an electron at the CNT and the hole at the PbSe having much longer lifetime. Observed ability to control the direction and the lifetime of the CT state makes the CNT/PbSe NW composites promising for photovoltaic applications.

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