Conformational analysis of some pyridinium phenolates and synthetic precursors based on X-ray and IR characterisations

Abstract

This manuscript reports X-Ray and IR characterizations of representative pyridinium phenolates, model compounds for nonlinear optics. These analyses reveal the close dependence existing between molecular structure and the contribution of quinone and zwitterionic limiting forms. The bond length alternation (BLA) values, the well-known parameter correlated to hyperpolarisability β, are also discussed and compared with literature data.

Computational Quantification of the Zwitterionic/Quinoid Ratio of Phenolate Dyes for Their Solvatochromic Prediction

“…Dyes 11-13 exhibited negative solvatochromic behavior [33,34], and their solvatochromic tendency was well-predicted by our theoretical model, with CT values accompanying the increase in the polarity of the medium. Finally, the CT values obtained for dyes 7 and 8 assigned them as negative solvatochromic compounds, again, in agreement with the spectral behavior they showed experimentally [31,32].…”

“…The solvatochromism of 7−9 varies with the degree of coplanarity between the phenolate and pyridinium groups [31], from a genuinely negative solvatochromism for dye 7, which presents the most hindered R substituents (R = i-Pr), to a non-linear negative solvatochromic behavior in the less steric hindered dye 8 (R = H). The analog 9 reported by Barzoukas et al [32] is a more annulated version of dye 8 and displays inverted solvatochromism, with an inversion point in dimethyl sulfoxide solution.…”

“…Molecules 2022, 27, 9023 9 of 14 classify dyes by predicting their experimental solvatochromism, and in the case of solvatochromically inverted dyes, predicting this behavior as a pass of the CT values from the quinoidal region (low part of the plot in Figure 5) to the zwitterionic region (up part of the plot in Figure 5), regardless of the accuracy of the polarity where this inversion takes place. The interplanar angle between the X and Y moieties controls the electronic coupling between these fragments, modifying the energy required for the charge transfer from one group to the other [31,39]. A high interplanar angle between the X and Y fragments will increase the charge separation, increasing the zwitterionic character of the ground state, ultimately showing the tendency of the dye to display negative solvatochromism.…”

Synthesis and Solvatochromic Behavior of Zwitterionic Donor–Bridge–Acceptor Systems with Oligo(p-phenylene) Spacers

“…39 The positive bond-length alternation value calculated with crystal-structure data for OPP(1)-O À suggests a predominantly quinoid-type structure. 38 In contrast, the small negative value calculated for [OPP(2)-O À ] 2 •HCl points to moderately zwitterionic character (Table S1, SI), likely due to the partial protonation.…”

“…The crystal structures of OPP(1)-OH and OPP(1)-O À have been reported previously. 38 In this work, single crystals of the elongated oligomers were obtained by slow diffusion of diethyl ether vapor into a solution of sodium methoxide in methanol or DMSO solution of compounds OPP(2)-OH and OPP(3)-OH. ORTEP representations of the obtained crystal structures are depicted in Figure 4 and derived parameters are given in Table S1 (SI).…”