Intercalation‐Induced Tunable Stimuli‐Responsive Color‐Change Properties of Crystalline Organic Layered Compound

Abstract

compound ( Figure 1 ). If the intercalation of guests changes crystal structures of the organic layered compound, the dynamic properties can be tuned by not molecular design but intercalation. In the present work, temperature-and stress-induced color-change properties of a crystalline layered PDA were tuned by intercalation of guest metal ions in the layered structure.PDAs with π -conjugated backbone are synthesized by polymerization of diacetylene (DA) monomers. [21][22][23] For example, 10,12-Pentacosadiynoic acid (PCDA) forms the layered crystal structure with the lamellar bilayer molecular assembly (Figure 1 ). When the distance between the diacetylene moieties is shorter than 0.5 nm in the assembled states, the topochemical polymerization without changes of the molecular arrangement is achieved by irradiation of UV light, X-ray, and γ-ray. [ 24,25 ] PDAs have a wide variety of applications, such as transistors and sensors. [26][27][28][29][30][31][32][33][34][35][36] One of the most characteristic properties of PDAs is stimuli-responsive color changes. [ 24,25 ] However, the stimuli-responsive properties of PDAs, such as color, responsivity, and reversibility, were not tuned by simple approaches except molecular design. In general, the blue color of PDA derivatives irreversibly turns to the red one by application of external stimuli, such as temperature rise. Since the external stimuli cause the torsion of the PDA main chains, shortening of the conjugation length induces the irreversible color changes. [26][27][28][29][30] The reversible color change was observed on the PDAs with the designed molecular structures. [ 37,38 ] The PDAs deposited on the specifi c substrates showed the reversible color changes. [ 39,40 ] The results imply that the structures of PDAs have an infl uence on the color-change properties. In our previous work, [ 41 ] the reversible color changes were observed with temperature increase and decrease on the thinfi lm crystals of the layered PDA with intercalation of zinc ion (Zn 2+ ) in the interlayer space. If the structures of the original PDAs are modifi ed by the intercalation, the color-change properties, such as color, responsivity, and reversibility can be tuned by the simple method. Here we focused on the intercalation of metal ions in the layered PDAs for tuning of the structures and the color-change properties. The metal salts of precursor PCDA crystals and their polymerized structures were prepared in the crystalline states and Langmuir-Blodgett

Two exfoliation approaches for organic layered compounds: hydrophilic and hydrophobic polydiacetylene nanosheets

“…1a and b ). 26 , 27 The topochemical polymerization of PCDA provides PDA without a change of the layered structure ( Fig. 1b and c ).…”

Toward Tunable Photonic Nanosheet Sensors: Strong Influence of the Interlayer Cation on the Sensing Characteristics

“…Current approaches rely mostly on the introduction of new materials or on their covalent modification . Approaches that introduce functionality through intercalants have received far less attention for applications in vapor sensing, despite showing very promising results in other sensing fields . For example, crystalline, layered polydiacetylene obtained from polymerization of 10,12‐pentacosadiyonic acid can be cation‐exchanged, which enhances its performance for temperature sensing …”

“…In addition to introducing new materials or covalent modifications, another very interesting way to tune the response of a sensor is by exchanging intercalating species, such as counter ions that intercalate into nanosheet stacks to compensate the layer charge . This has been demonstrated for nanocellulose‐based sensors to differentiate liquids and in bulk layered materials, mainly clays, with luminescent intercalants used to detect liquids or vapors .…”

Polydiacetylene‐Tb3+ Nanosheets of Which Both the Color and the Fluorescence Can Be Reversibly Switched between Two Colors

“…Since the radius of Tb 3＋ ions is about 0.09-0.11 nm, [40] the increment of interlayer distance was not simply ascribed to the diameter of the Tb 3＋ ions, but also due to the conformational change of PDA side chains after the intercalation of Tb 3＋ ions, which was also demonstrated in previous report. [41] The interaction between the Tb 3＋ ions and the carboxyl groups at the end of PDA side chains was proved to be coordination interaction (demonstrated below). Such intercalated structure resulted in the significant increase of the melting point of PCDA-Tb 3 ＋ crystalline nanosheets comparing with PCDA crystals.…”