SHG Active Salts of 4-Nitrophenolate with H-Bonded Helical Formations:  Structure-Directing Role of ortho-Aminopyridines

Abstract

Among the several approaches developed for the fabrication of molecular crystals with noncentrosymmetric lattices, incorporation of chirality is the only one which guarantees it for fundamental symmetry reasons. One of the few quadratic nonlinear optical chromophores which form a large number of noncentric cocrystals/salts without the assistance of chirality is 4-nitrophenolate; hence it is an ideal candidate to explore new avenues to noncentric lattice formation. The utility of a structure-directing counterion in such an approach is explored in the present study. In contrast to para-aminopyridine, it is found that ortho-aminopyridines (2-aminopyridine and 2,6-diaminopyridine) which support bent pathways of supramolecular assembly through H-bond formation lead to noncentric cocrystalline salts with 4-nitrophenol. The molecular assembly in the crystals can be visualized in the form of H-bonded helical structures. The second harmonic generation observed in the new materials is analyzed in terms of the contributions from the partners in the ternary system consisting of 4-nitrophenolate, pyridinium, and 4-nitrophenol.

Growth and characterization of a nonlinear optical crystal—2,6-diaminopyridinium 4-nitrophenolate 4-nitrophenol (DAPNP)

“…The SHG efficiency of the grown crystal was 11.5 times (the insert in Fig. 6) that of urea (close to the data reported by literature [20]). Fig.…”

“…However, organic molecular crystals show a strong predilection toward centrosymmetric organization structure. In the past decades, many approaches have been developed to acquire noncentrosymmetric crystals [17][18][19][20] in which one way to include both ionic and hydrogen-bonding interactions in a system is to form ionic co-crystals from proton transfer between an organic acid and organic base [21][22][23]. 4-nitrophenolate (NP-) with a typical one-dimensional (1D) donor-acceptor p system and the proton transfer of phenolic OH with various organic and inorganic bases results in the increasing of hyperpolarizability of both species has been used to form a large number of noncentrosymmetric structures with the achiral counterions [24][25][26][27][28][29][30].…”

“…Thus, the 4-nitrophenolate and pyridine are expected to form ionic co-crystals by proton transfer through H-bonding interactions. 2,6-diaminopyridinium 4-nitrophenolate 4-nitrophenol (DAPNP) with high second harmonic generation (SHG) efficiency had been reported by Prakash and Radhakrishnan [20], and it is an ionic crystal in which the 4-nitrophenolate anion and the 2,6-diaminopyridinium cation result from proton transfer and neutral 4-nitrophenol stands as a third partner. DAPNP crystal will be a good candidate for NLO materials, and here we report for the first time the bulk growth, thermal properties, optical, dielectrical and of this material.…”

Hexafluorosilicates of bis(aminopyridinium). The relationship between H-bonding system and solubility of salts

“…The present communication continues the previous investigations and is devoted to the study of relationship between the composition and some properties of aminopyridinium hexafluorosilicates. Both 2-aminopyridine and 2,6-diaminopyridine are very popular co-crystal formers in supramolecular chemistry of anions [17,18]. In contrast to para-aminopyridine, it is found that ortho-aminopyridines (2-aminopyridine and 2,6-diaminopyridine) support bent pathways of supramolecular assembly through Hbond formation as the amino and pyridinium groups together form a kind of ''angle joint'' [17] and serve as an efficient molecular tecton for the intermolecular assembly supported by hydrogen bonding and in some cases can lead to noncentric cocrystalline salts.…”

New organic binary solids with phenolic coformers for NLO applications

“…The combination of these components resulted in strong hydrogen bonding and the proton transfer that increases the molecular hyperpolarizability [19][20][21]. In the 4-nitrophenol molecule the phenolic group exhibits amphoteric properties acting as hydrogen-bond donor through the hydroxyl H-atom, and electron-donor as well through the oxygen atom lone pair, while the nitro-group is displaying the electron-and hydrogen-bond acceptor properties.…”