First-principles study of salicylideneaniline molecular crystals: Tautomerization reaction involving intermolecular hydrogen bonds

Abstract

Salicylideneaniline molecular crystals, in which tautomerization reactions involving intermolecular hydrogen bonds take place under photoirradiation, are investigated by using the first-principles calculation based on density-functional theory. Structures and properties of the two crystal phases, enol form with intramolecular hydrogen bonding and trans-keto form with intermolecular hydrogen bonding, have been theoretically examined from the viewpoint of atomic bonding pattern. The present calculation result indicates that the trans-keto form, which is somewhat different from a former X-ray analysis result, appears close to a quinoidal form rather than a zwitterionic form. Analysis of energetics in gas and solid phases and differential electron density indicate that stabilization of the crystalline trans-keto form can be realized by intermolecular hydrogen bonds electrostatically reinforced by charge redistribution that is induced by packing the molecules in solid state. These findings lead to a mechanism in which the quinoidal trans-keto form in crystalline phase may exhibit extraordinary stabilization as experimentally observed. Furthermore, dielectric permittivity tensors of the molecular crystals have been calculated on the basis of density-functional perturbation theory. The calculation result indicates that the photodriven tautomerization reaction induces sufficient change of the refractive indices advantageous to various applications such as photochromic memory or switch.

Insights into the Origin of Solid‐State Photochromism and Thermochromism of N‐Salicylideneanils: The Intriguing Case of Aminopyridines

“…[13b] The extraordinary stability of the NH form in the crystalline state was explained by the presence of a resonance hybrid of two canonical structures (non-polar quinoidal and polar zwitterionic forms). [15] In the present case such a hybrid cannot be excluded. Interestingly, this experiment demonstrates that the presence of bulky tert-butyl groups on the phenol group is not necessary to obtain a high thermal stability for the trans-keto form.…”

“…[15] In the present case such a hybrid cannot be excluded. Interestingly, this experiment demonstrates that the presence of bulky tert-butyl groups on the phenol group is not necessary to obtain a high thermal stability for the trans-keto form.…”

“…[14] N-Salicylideneaniline derivatives belong to a class of molecules that exhibit photochromism as well as thermochromism in the crystalline state. [15] Earlier classification of N-salicylideneaniline derivatives were based on their thermochromic or photochromic properties. [16][17][18] However, this classification was recently revised with molecules considered as being either exclusively thermochromic, or thermochromic and photochromic.…”

A Spectroscopic Study of Tautomeric Equilibrium of Salicylideneaniline in ZSM-5 Zeolites

“…Among molecules belonging to the Schiff base family, N-salicylideneaniline (SA) is a model compound largely studied in both the solid state [ 1 , 2 , 3 , 4 , 5 ] and solutions with various solvents [ 3 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. Due to its photochromic, thermochromic and solvatochromic properties, this molecule is of significant interest for potential applications in various domains from optical devices [ 14 , 15 , 16 ] and molecular switches [ 17 , 18 , 19 ] to medicine [ 20 , 21 , 22 ].…”

Potential Energy Surfaces and Quantum Yields for Photochromic Diarylethene Reactions

“…Many groups have reported experimental research devoted to improving various critical properties of DAEs [ 3 , 4 ], and we have reported theoretical studies devoted to: (i) explaining the origin of thermal stability [ 5 , 6 ]; (ii) designing absorption wavelengths [ 7 ]; (iii) identifying the factors determining the quantum yield for photochromic isomerization [ 8 ]; (iv) evaluating a variety of experimental spectroscopic data (NMR [ 9 , 10 ], Raman [ 11 ], IR [ 12 , 13 , 14 , 15 ], and ESR [ 16 , 17 ]); (v) finding applications that utilize hole and electron transport properties [ 18 ]; (vi) designing the environmental field effect around the molecule (solvent [ 9 ]; polymer [ 19 ] and crystal [ 20 ]), and (vii) elucidating nonlinear response properties [ 21 ].…”