The recent discovery of temporally controlled gels opens broad perspectives to the field of smart functional materials. However, to obtain fully operative systems, the design of simple and robust gels displaying complex functions is desirable. Herein, we fuel dissipative gelating materials through iterative additions of trichloroacetic acid (TCA). This simple fuel enables to switch over time an acid/base-dependent commercially available amino acid gelator/DBU combination between three distinct states (anionic, cationic, and neutral), while liberating volatile CO 2 and CHCl 3 upon fuel consumption. Of interest, the anionic resting state of the system is obtained through trapping of 1 equiv of CO 2 through the formation of a carbamate. The system is tunable, robust, and resilient over time with over 25 consecutive sol−gel−sol cycles possible without significant loss of properties. Most importantly, because of the chiral nature of the amino acid gelator, the system features chiroptical switching properties moving reversibly between three distinct states as observed by ECD. The described system considerably enhances the potential of smart molecular devices for logic gates or data storage by adding a time dimension based on three states to the gelating materials. It is particularly simple in terms of chemical components involved, but it enables sophisticated functions.
Smart materials reversibly changing properties in response to a stimuli are promising for a broad array of applications. In this article, we report the use of trichloroacetic acid (TCA) as fuel to create new types of time-controlled materials switching reversibly from a gel to a solution (gel–sol–gel cycle). Applying various neutral amines as organogelators, TCA addition induces amine protonation, switching the system to a solution, while TCA decarboxylation over time enables a return to the initial gel state. Consequently, the newly obtained materials possess interesting time-dependent properties applied in the generation of remoldable objects, as an erasing ink, as chiroptical switches, or for the generation of new types of electrical systems.
Dissipative systems are based on the supply of energy to a system by fuel pulses and dissipation of this energy through the fuel decomposition, resulting in repetition of a given physical or biological function. Such out of equilibrium processes are at the heart of all living organisms, and in the past decade, researchers have attempted to transpose these principles to purely synthetic systems. However, upon fuel decomposition, the resulting waste generated tends to accumulate in the system, rapidly inhibiting the machinery after a few cycles of fuel pulses. In order to solve this issue, trichloroacetic acid has appeared as a fuel of choice to reversibly change the acidity of a system, liberating volatile chloroform and CO2 upon fuel decomposition. In this Perspective, we present the advantages of this fuel and successful applications ranging from conformational switches to rotary motors to temporal control over crystallization or smart materials.
Amine purification have for long been dominated by tedious stepwise processes involving the generation of large amounts of undesired waste. Inspired by recent work on out of equilibrium molecular machinery, using trichloroacetic acid (TCA), we disclose a purification technique considerably decreasing the number of operations and the waste generation required for such purifications. At first, TCA triggers the precipitation of the amines through their protonated salt formation, enabling the separation with the impurities. From these amine salts, simple decarboxylation of TCA liberates volatile CO2 and chloroform affording directly the pure amines. Through this approach, a broad range of diversely substituted amines could be isolated with success.
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