Manipulation of Liquid Crystalline Properties by Dynamic Covalent Chemistry─En Route to Adaptive Materials

Abstract

Dynamic covalent bonds bear great potential for the development of adaptive and self-healing materials. Herein, we introduce a versatile concept not only for the design of low-molecular-weight liquid crystals but also for their in situ postsynthetic modification by using the dynamic covalent nature of imine bonds. The methodology allows systematic investigations of structure–property relationships as well as the manipulation of the materials’ behavior (liquid crystallinity) and the introduction of additional properties (here, fluorescence) by a solvent-free method. For the first time, the transamination reaction is followed by variable-temperature 19F solid-state NMR in the mesophase, providing insights into the reaction dynamics in a liquid crystalline material. Finally, the application potential for the design of liquid crystalline materials with adaptive properties is demonstrated by a sequential combination of these reactions.

Tuning the Fluorescence in Dynamic Covalent Bonded Liquid Crystals

“…The backward reaction by mixing ImCl and 4-nitroaniline in a 1:1 ratio revealed the same percentage as in the forward reaction. This proves the system is in its equilibrium state and is in accordance with previously reported systems …”

“…31−33 Recently, our group reported a concept for adaptive liquid crystalline materials making use of the dynamics of the imine bond. 34 Thereby, the liquid crystalline behavior was modified in situ by exchange or metathesis reactions giving rise to a sustainable approach toward novel materials design.…”

“…They utilized nitro-substituted pyrrolopyrrole derivatives to obtain LC materials which show an increase in fluorescence intensity in the liquid crystalline state compared to the crystalline or isotropic state . Adaptation to external stimuli is an important feature of living matter and a source of inspiration for materials’ scientists. − Recently, our group reported a concept for adaptive liquid crystalline materials making use of the dynamics of the imine bond . Thereby, the liquid crystalline behavior was modified in situ by exchange or metathesis reactions giving rise to a sustainable approach toward novel materials design.…”

Surface‐Enforced Alignment of Reprogrammable Liquid Crystalline Elastomers

“…[ 35 , 36 , 37 , 38 , 39 , 40 , 41 ] CANs have been implemented in LCEs as a method for both shape retention upon actuation and (re)programming of complex deformations. [ 42 , 43 , 44 , 45 ] Notably, numerous chemistries composed of acrylates and dithiols have been used in these dynamic systems, often taking advantage of the thiol‐Michael oligomerization step, but thus far none have been incorporated in surface‐aligned LCEs. [ 46 , 47 , 48 , 49 , 50 , 51 ] While these previous demonstrations utilize mechanical alignment, allowing for assessment of dynamic bond programming in a wider range of film thicknesses than can be achieved with surface enforced alignment (limited to ≈50 µm), [ 47 , 52 ] the surface alignment approach enables much higher spatial resolution of directed mesogen orientation.…”

Functional Liquid Crystal Elastomers Based on Dynamic Covalent Chemistry

“…Furthermore, adding 4‐hydroxybenzaldehyde derivatives further endowed them with fluorescent properties. The results disclosed in this study would lead to different strands of potential applications in liquid‐crystalline DCC systems and photonic sensing [110] …”