A simple diagnostic test based on orbital overlap [M. J. G. Peach et al., J. Chem. Phys., 2008, 128, 044118] may be used to help judge the reliability of excitation energies in time-dependent density functional theory (TDDFT) when using generalized gradient approximation (GGA) and hybrid functionals. Orbital plots are used to illustrate the test for a model tripeptide and for 4-(N,N-dimethylamino)benzonitrile, which are representative of systems containing low- and high-overlap charge-transfer excitations. The scheme is then applied to a series of triazene chromophores in solvent, highlighting the relationship between overlap and oscillator strength and its implications for theoretical absorption spectra. No low-overlap excitations are observed with a hybrid functional; a single one is identified using a GGA. To assess the diagnostic test and to judge functional performance, gas phase triazene TDDFT excitations are compared with correlated ab initio values. The diagnostic test correctly identifies two low-overlap problematic GGA excitations. However, it does not identify another problematic excitation where the electron is excited to a spatially extended orbital, which necessarily has reasonable overlap with the occupied orbital; an improved diagnostic quantity is required for such cases. The best agreement between TDDFT and correlated ab initio excitations is obtained using a Coulomb-attenuated functional; the errors are significantly smaller than from the GGA and hybrid functionals. The study provides further support for the high quality excitations from Coulomb-attenuated functionals, negating the need for diagnostic tests.

Time-dependent Hartree-Fock and Møller-Plesset second-order calculations have been used to unravel the relationships between structure and first hyperpolarizability in spiropyran/merocyanine couples and therefore to design efficient second-order nonlinear optical switching compounds. Large first hyperpolarizabilities for the merocyanine form as well as large contrasts of first hyperpolarizability have been obtained when, on the same species, (i) substituents at R(1) and R(2) positions on the phenolate ring of the merocyanine form are strong acceptor and donor substituents, respectively, (ii) the ethylenic bridge is substituted by donor groups, (iii) the other aromatic part of the system is benzimidazolo rather than indolino or benzothiazolo, and (iv) strong donor substituents are placed on the benzimidazolo moiety.

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The influence of the capacitive (E)-to-inductive transition (H) in inductively coupled plasma discharges is investigated for propanethiol plasma polymerization. In the E mode, at low plasma density, the sulfur content in the layers, measured by XPS, is quite high and strongly decreases after aging in the air. This phenomenon is attributed to the desorption of trapped sulfur-based molecules (e.g., H 2 S). In the H mode, presumably higher surface temperature prevents the trapping scenario during the layer growth and, as a consequence, yields a lower sulfur content which is stable after aging. Mass spectrometry measurements reveal important variations of the plasma chemistry depending on the discharge mode. The major change concerns the complete disappearance of the precursor in the H mode accompanied by the large production of CS 2 molecules. Furthermore, a linear correlation is found between the concentration of the CS 2 species and the atomic sulfur content in the Hmode synthesized layers. In addition, based on DFT calculations, different pathways of fragmentation are proposed as a function of the plasma parameters. The whole set of results highlight the importance of the E−H transition for the growth of thiol-based plasma polymers.