Playing with Isomerism: Cocrystallization of Isomeric N-Salicylideneaminopyridines with Perfluorinated Compounds as Halogen Bond Donors and Its Impact on Photochromism

Abstract

In N-salicylideneaniline derivatives, photochromism occurs by a two-step isomerization mechanism. Photochromism has been reported to be closely related to the molecular conformation of the N-salicylideneanilines (described by the dihedral angle Φ) and to the free available space (V free ) in the crystal. In this contribution, we focus on cocrystals of isomeric Nsalicylideneaminopyridines with perfluorinated halogen bond donors as coformers. The advantage of working with isomers is that they have a similar (if not equal) molecular volume. This aspect means that the evaluation and comparison of the free available spaces within cocrystals is not affected by the differences in the molecular volumes of their constituents. Cocrystals were synthesized by a one-pot procedure, which allowed concomitant formation of covalent (imine) and noncovalent (halogen) bonds. Each cocrystal was characterized by X-ray diffraction, and its photochromism was assessed by UV−vis diffuse reflectance. Our results suggest that the Φ/V free model grossly oversimplifies the complexity of the dynamic phenomenon behind the photoisomerization of N-salicylideneanilines. For the above-mentioned reasons, careful examination of intermolecular interactions and crystals packing (localization of voids, evaluation of intermolecular interactions and stacking modes) should be taken into account and used to supplement the current proposed model based on Φ and V free .

Intermolecular Interactions in Functional Crystalline Materials: From Data to Knowledge

“…At the same time, it was demonstrated that C=O and C-Br groups compete with each other for the most acidic hydrogen atoms, thus that FIM predictions of synthons based on C-H...Br bonding became less reliable at the presence of C-H...O=C bonding [257]. At the absence of carbonyl groups the FIMs for the N-salicilidenanylines probed with C-I and C-F groups successfully predict all of the C-I...N and many of the C-F...H-C interactions in co-crystals of N-salicilidenanylines with perhalogenated co-formers [259]. Mugheirbi and Tajber analyzed the FIM hotspots around the itraconazole molecule to understand the molecular environment in the mesophase [260].…”

Tautomeric Equilibrium of an Asymmetric β-Diketone in Halogen-Bonded Cocrystals with Perfluorinated Iodobenzenes

“…This has led to the question of whether the halogen bond-an interaction in many ways similar to hydrogen bond [27][28][29][30]-can have a similar effect on the intramolecular hydrogen transfer and stabilization of the keto-amino tautomer. Unfortunately, despite the research on halogen bonded o-hydroxyimine systems performed to date [31][32][33][34][35][36][37], the answer to this question remained inconclusive. The possible reason for this is that the stabilizing effect of the halogen bond might be too subtle to noticeably affect proton transfer through the highly asymmetric O-H•••N hydrogen bond.…”

Synthesis, crystal structure and conformational analysis of an unexpected [1,5]dithiocine product of aminopyridine and thiovanillin

“…As part of our interest in photo-and thermochromic cocrystals (Carletta et al, 2015(Carletta et al, , 2016(Carletta et al, , 2018, the investigation of compounds analogous to the already studied N-salicylideneaniline derivatives of o-vanillin could lead to a better understanding of the factors influencing photo-and thermochromic behaviour. Indeed, the impact of the intramolecular hydrogen bond with regard to external stimuli (temperature and light) should affect the properties of new analogues.…”