International audienceAlthough copper thiocyanate (CuSCN) shows potential as a substrate for p-type dye sensitised solar cells, its interaction with organic anchoring groups remains largely unexplored. In this ab initio study, we provide atomistic insight into how CuSCN surfaces interact with a series of nitrogen-based (pyridine, aniline, phenanthroline, benzenediamine) and sulfur-based (thiophenol, thiophenoxide, thiocatechol) anchoring groups. We profile several low-index surfaces, including both polar and nonpolar cleavages, to determine their stabilities and electronic structures. In screening these surfaces for the most favourable adsorption modes and binding sites for organic anchors, we found that adsorption is chiefly driven by the propensity of surface copper atoms to restore a tetrahedronal coordination environment. We show that the majority of the tested anchors, even the bidentate structures, exhibit low binding energies on CuSCN, which illustrates how chemical intuition may be misleading for identifying the ideal anchors on the basis of nucleophilicity and denticity alone. By pinpointing the causes of modest adsorption energies, we present hints as to how adsorption strength and alignment of the organic-inorganic states can be improved on CuSCN
International audienceThe present contribution constitutes an extensive density functional theory (DFT) investigation of the nonlinear optical (NLO) properties of a large number of molecules belonging to the azobenzene and azothiophene families of photochromic compounds which can act as NLO switches. Toward the design of systems simultaneously presenting both large total nonlinear response values, beta(tot), and large contrast, beta(ratio), between the cis and trans isomers, we have focused not only on the monomers but also on azobenzene dimers, the latter containing two N=N bonds along the molecular backbone. After it was established that the inclusion of implicit solvation is not important in drawing qualitative conclusions on the NLO switching ability for the investigated systems, gas-phase calculations have shown that for the asymmetric pushpull azobenzene and azothiophene candidates, the combination of strong donating groups such as NPh2, N(Ph-OMe)(2), and N(Ph-NMe2)(2) with the dicyanoethene group CH=C(C=N)(2) as an acceptor delivers large ?trans (150-217 x 10(-30) esu) and non-negligible beta(cis) (18-55 x 10(-30) esu) values as well as substantial contrast, beta(ratio) (3.9-8.7). For the investigated double azobenzenes, it is found that, with a careful choice of donor and acceptor groups, the contrast, beta(ratio), can be significantly increased compared to that of the monomers while maintaining large beta values that facilitate their detection with standard experimental techniques (e.g., electric-field-induced second-harmonic generation). Our results set the stage on which further theoretical and experimental studies can be based in the search for efficient and versatile NLO switches
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