Dynamic Vapochromic Behaviors of Organic Crystals Based on the Open–Close Motions of S‐Shaped Donor–Acceptor Folding Units

Abstract

The first vapochromic organic crystals are described with respect to their preparation, color change, adsorption/desorption properties, crystal structures, and color-change mechanism. Non-solvatochromic, 1,4,5,8-naphthalene-tetracarboxylic diimide (NDI) derivatives 1 a bearing two pyrrole imine (PI) tethers have been used as a motif for the crystal packing template. Red-purple vapochromic solid 3 was prepared by evacuation of orange crystals 2 (equivalent to 1 a2 MeOH), obtained by recrystallization of 1 a from MeOH. Solid 3 showed high-adsorption ability and unprecedented vapor-dependent color changes upon exposure to a variety of organic vapors, whereas light brown amorphous solid 1 a, did not show vapo- or solvatochromic behavior toward any organic solvent. The strong adsorption capability of 3 was confirmed by TGA experiments and adsorption/desorption isotherms. Analysis of the solid-state UV/Vis analysis revealed that the vapor-dependent color changes of 3 were owed to the specific interference of solvent vapors with its broad CT absorbance at lambda=450-650 nm. Packing structures of 1 a in orange crystals 2, red-purple solid 3, and regenerated orange solid 2 were unequivocally established by single crystal and synchrotron powder X-ray diffraction, respectively. Molecular structures and arrays of 1 a in these materials indicated that 1) unit 1 a had an S-shaped folded conformation in 2 and 3 by intramolecular donor-acceptor interactions between NDI and two PI units; 2) inclusion of the guest vapor into the S-shaped template decreased the intramolecular PI-NDI interactions, accompanied by increasing intermolecular NDI-NDI and PI-PI interactions; and 3) such flexible, open-close motions of the S-shaped template could be repeated during reversible adsorption/desorption processes without degradation of crystal packing. The adsorption properties and mechanism of molecular shape-dependent vapochromic behavior of 3 are discussed with reference to experimental results, crystallographic data, and theoretical calculations.

Spectroscopic Probing of the Dynamic Self‐Assembly of an Amphiphilic Naphthalene Diimide Exhibiting Reversible Vapochromism

“…[11] Although, vapochromism has been recently observed in elegantly designed NDI organic crystals, [12] there is no report pertaining to vapo-responsive NDI nanostructures, as shown here. We show here that this remarkable vapochromic behavior of NDI-Amph is due to a dynamic reorganization in molecular arrangement from a J-type self-assembly to a fluorescent preassociated H-type excimer state.…”

Controlling Crystal Structures and Multiple Thermo‐ and Vapochromic Behaviors of Benzimidazole‐Based Squaraine Dyes by Molecular Design and Solvent Adjustment

“…Recently,v apochromic materials have attracted increasing attentionb ecause of their promising applicationsi nt he analytical, environmental, optical, biochemical,a nd electronic areas. [16] Nevertheless,only af ew studies on the vapochromism of organic crystals exist, [17] probablyb ecause of the absence of the do rbitali nteractions neededf or versatile color change. [16g] Considering that the emission properties of SQB in the aggregated state are strongly dependento nt he molecular packing modes, which in turn are affectedb yt he solvent, alteration of such arrangements through the loss andg ain of solventm olecules may induce changes in their fluorescent properties.…”

Vapochromism of Organic Crystals Based on Macrocyclic Compounds and Inclusion Complexes

“…In 2010, Naota et al [32] proposed the first vapochromic organic crystals based on naphthalenediimide (NDI) derivatives ( Figure 6). They designed S-shaped NDI derivatives bearing two pyrrole-imine tethers via an alkyl chain (6).…”