Integrated NMR and Computational Study of Push–Pull NLO Probes: Interplay of Solvent and Structural Effects

Abstract

In this study we combined QM calculations and NMR measurements to understand at a detailed level the complex interplay of structural/electronic properties with the effects of the solvent in the NLO activity of push-pull systems, quantified in terms of variations of the static hyperpolarizability. Different parameters (bond lengths and bond length alternation, vibrational frequencies, electronic charge distribution) are introduced and tested to rationalize both the solvent sensitivity of three molecular systems (namely, p-nitroaniline, ethyl 4-ammino benzoate, and 5-nitro-1H-indole) and the differences among them. This analysis has finally allowed us to establish a clear correlation between the charge transfer behavior of the systems, their NLO properties, and NMR parameters also validating simplified but effective chemical analyses based on resonance limit forms.

Solvent‐Dependent Structure of Iridium Dihydride Complexes: Different Geometries at Low and High Dielectricity of the Medium

“…Little is known, however, about changes in the structures of the molecules, because features of the NMR, UV/Vis and vibrational spectra that may be attributed to medium effects do not provide such information directly, and because it is not easy to separate specific solvation effects from non‐specific. Computational studies at various levels of theory typically indicate relatively minor structural changes of around 0.01–0.02 Å or less upon changing the medium (under certain conditions up to 0.08 Å), which nevertheless are believed to have an important impact on the spectroscopic properties.…”

NMR Spin–Spin Coupling Constants in Polymethine Dyes as Polarity Indicators

“…The chemical shifts of the 13 C nuclei that are connected to the donor and acceptor groups in such systems are known to be sensitive to the nature of the molecular geometry (i.e., neutral, cyanine‐like, zwitterionic, etc.) and have thus been proposed to be useful for a qualitative assessment of different molecular forms 44–48. The difference in the chemical shifts for carbon atoms that are connected to donors and acceptors has been shown to increase with solvent polarity 48.…”

“…and have thus been proposed to be useful for a qualitative assessment of different molecular forms 44–48. The difference in the chemical shifts for carbon atoms that are connected to donors and acceptors has been shown to increase with solvent polarity 48. However, this value only conveys the information that the shielding of the donor‐group carbon atom increases with solvent polarity and that the shielding of the acceptor‐group carbon atom decreases with increasing solvent polarity and, hence, it cannot be used to identify the conformational nature of the probe in different solvents.…”

From Graphene to Carbon Nanotubes: Variation of the Electronic States and Nonlinear Optical Responses

“…[39][40][41] Moreover, it has been proven that CAM-B3LYP is better for calculating the first hyperpolarizability of p-conjugated systems than other methods. [42] It has been widely adopted to predict the molecular properties in charge-transfer processes [43][44][45] and was employed to evaluate the static first hyperpolarizabilities with the 6-31G(d) basis set in the present work.…”