Experimental and Theoretical Insights into the Optical Properties and Intermolecular Interactions in Push‐Pull Bromide Salts

Abstract

Experimental and theoretical insights into the nature of intermolecular interactions and their effect on optical properties of 1‐allyl‐4‐(1‐cyano‐2‐(4‐dialkylaminophenyl)vinyl)pyridin‐1‐ium bromide salts ( I and II ) are reported. A comparison of optical properties in solution and in the solid‐state of the salts ( I and II ) with their precursors ( Ia and IIa ) is made. The experimental absorption maxima (λ max ) in CHCl 3 is at 528 nm for I and at 542 nm for II , and a strong bathochromic shift of ∼110 nm is observed for salts I and II compared with their precursors. The absorption bands in solid‐state at ∼627 nm for I and at ∼615 nm for II that are assigned to charge transfer (CT) effect. The optical properties and single crystal structural features of I and II are explored by experimental and computational tools. The calculated λ max and the CT are in good agreement with the experimental results. The intermolecular interactions existing in the crystal structures and their energies are quantified for various dimers by PIXEL, QTAIM and DFT approaches. Three types of interactions, (i) the cation⋅⋅⋅cation interactions, (ii) cation⋅⋅⋅anion interactions and (iii) anion⋅⋅⋅anion interactions are observed. The cationic moiety is mainly destabilized by C−H⋅⋅⋅N/π and π⋅⋅⋅π interactions whereas the cation and anion moiety is predominantly stabilized by strong C−H⋅⋅⋅Br − interactions in both structures. The existence of charge transfer between cation and anion moieties in these structures is established through NBO analysis.

Weak noncovalent interactions in two positional isomers of acrylonitrile derivatives: inputs from PIXEL energy, Hirshfeld surface and QTAIM analyses

“…The remaining two of them are H•••H contacts (H-H bonding) formed between H atoms of rings A and B and between vinylic CH and H atom of the ring C (Figure 3A). The former H-H bonding and C-H•••C contacts were observed in closely related structures repored earlier (Venkatesan et al, 2018;Udayakumar et al, 2019cUdayakumar et al, , 2019bUdayakumar et al, , 2020. The importance of the non-electrostatic origin of the H-H bonding has been discussed elsewhere (Matta et al, 2003;Al-Ghulikah et al, 2020;El-Emam et al, 2020).…”