Influence of the Alkyl Side Chain Length on the Assembly and Thermochromic Solid-State Properties in Symmetric and Asymmetric Monoalkoxynaphthalene–Naphthalimide Donor–Acceptor Dyads

Abstract

We have been investigating monoalkoxynaphthalene–naphthalimide (MAN–NI) donor–acceptor dyads that undergo a unique and dramatic orange-to-yellow thermochromic transition in the solid state. This study reports a new series of these stimuli-responsive solids, based on dyads with symmetric and relatively long alkyl side chains, as well as asymmetric derivatives. The length of the alkyl side chains influenced the structures, properties, and dynamic behavior of the resulting solids. All of the symmetric alkyl side chain derivatives can crystallize with identical packing (allowing for alkyl chain length differences) in a lasagna-like fashion with alternating alkyl and stacked aromatic layers. The fully extended alkyl side chains are aligned in an interdigitated, “cork and bottle” fashion. The aromatic layers feature head-to-head stacking geometries of the aromatic dyad cores. The crystalline solids derived from each of these derivatives undergo dramatic thermochromic orange-to-yellow transition in the solid state. Crystal structures were obtained for three of the four asymmetric dyad derivatives. In each case, layered structures were observed, although the mismatch in alkyl side chain lengths results in a unique hybrid alkyl/aromatic layer. Two of the asymmetric derivatives exhibit almost identical head-to-head dyad core stacking geometries, while one exhibits a head-to-tail dyad core stacking geometry. Of the four asymmetric dyads studied, only two asymmetric derivatives with the longer alkyl side chains exhibit dynamic solid-state behavior. Overall, our results demonstrate the relatively general nature of the thermochromic orange-to-yellow color-changing mechanism of the MAN–NI dyads and verify the link between the alkyl side chain interactions and this interesting stimuli-responsive behavior in the solid-state.

Self‐Assembly of Discrete Multi‐Chromophoric Systems

“…By applying light and mechanical stimuli, the dyad 36 also displayed different colours (Figure 8c). Another set of stimuli responsive dyads based on monoalkoxynaphthalene‐naphthalimide (MAN‐NI) donor‐acceptor system was reported by Iverson and co‐workers in 2022 [51] . These dyads 37 (Figure 8d) exhibited an orange to yellow thermochromic transition in the solid state.…”

“…Another set of stimuli responsive dyads based on monoalkoxynaphthalenenaphthalimide (MAN-NI) donor-acceptor system was reported by Iverson and co-workers in 2022. [51] These dyads 37 (Figure 8d) exhibited an orange to yellow thermochromic transition in the solid state. They studied the influence of alkyl side chain length on the self-assembly and thermochromic properties of symmetric and asymmetric derivatives of this multi-chromophoric system.…”

π-Stacking among the Anthracenyl Groups of a Copper Complex Resulted in Doubling of Unit Cell Volume To Provide New Polymorphs

“…19 The spatial organization of stacks among aromatic planes controlled by a flexible part shows an effect on photoluminescence. 20 We felt that a compound having unsymmetrical aromatic group such as the anthracenyl-group will be suitable to explore stacks among anthracenyl groups which may adopt lamellar or Herringbone arrangements, as shown in ix and x of the unidirection linear chains maintaining the slanting orientations to result lamellar structure or in the opposite directions to provide a Herringbone structure. These arrangements could lead to polymorphs but there has been no systematic approach available to obtain them, so we followed a design principle to organize stacks of π-components of a cationic part in layered anionic arrangements.…”

“…The stacking arrangements of molecules differ from system to system and can result in different types of stacking arrangements, among which the Herringbone or lamellar structures have been known to provide independent properties originating from packing patterns . The spatial organization of stacks among aromatic planes controlled by a flexible part shows an effect on photo-luminescence . We felt that a compound having unsymmetrical aromatic group such as the anthracenyl-group will be suitable to explore stacks among anthracenyl groups which may adopt lamellar or Herringbone arrangements, as shown in ix and x of the Figure b.…”

“… 19 The spatial organization of stacks among aromatic planes controlled by a flexible part shows an effect on photo-luminescence. 20 We felt that a compound having unsymmetrical aromatic group such as the anthracenyl-group will be suitable to explore stacks among anthracenyl groups which may adopt lamellar or Herringbone arrangements, as shown in ix and x of the Figure 1 b. There are three important requirements to observe such stacking patterns; (a) face-to-face stacks among the planar rings, (b) inclined stacks in the same direction with respect to a vertical axis, (c) there must be organized, unidirection linear chains maintaining the slanting orientations to result lamellar structure or in the opposite directions to provide a Herringbone structure.…”