INTRODUCTION

Solvent-free methodologies for materials synthesis and processing represent critical aspects in the pursuit of environmentally sustainable chemistry [1–5]. Topochemical polymerization (TCP), dictated by the geometric arrangement of reactant molecules within crystal lattices, has emerged as a powerful strategy for solid-state polymer synthesis [6–13]. This approach enables the controlled formation of stereoregular polymers that are often difficult to achieve through traditional solution-phase chemistry, where high molecular freedom permits diverse reaction pathways [14–24]. Recent decades have witnessed burgeoning advancements in the design of organic crystals tailored specifically for TCP, facilitating their utility in sustainable materials, responsive systems and energy-related applications [25–34]. Typically, TCP relies on the preorganization of molecules within crystal lattice, wherein reactive groups are placed in close proximity and oriented to facilitate optimal orbital overlap (Fig. 1a) [35–39]. Specific functional groups or intermolecular interactions have been used to promote favorable crystalline arrangements [40–46]. However, the exact packing of molecules in crystals is challenging to manipulate in a predictable fashion due to the intricate interplay of weak intermolecular interactions [47,48]. As such, the design of suitable molecular crystals for TCP is largely empirical, as even a slight chemical modification can unpredictably influence the carefully arranged molecular packing [49–51]. Therefore, the lack of broad applicability presents a substantial obstacle for the practical utilization of TCP.

Figure 1.: General considerations of topochemical polymerization (TCP). (a) Schematic representation of the stringent constraints required for topochemical reaction in rigid crystal lattices. (b) Flexible conditions for topochemical reaction in LC state due to the dynamic molecular motions. (c) Chemical structures of the three-armed CS discotic LC monomers 1–6. The self-assembled core-shell columnar LC structures promote axial TCP via [2 + 2] cycloaddition of the CS cores, while the aliphatic shells prevent intercolumnar crosslinking, leading to the formation of linear helical polymers. The letters (a, a’, b, etc.) indicate protons with 1H NMR chemical shifts marked in Fig. 2c.

To circumvent these limitations and advance the development of a more versatile TCP framework, it is necessary to devise a method that accommodates a broader range of permissible molecular alignments in ordered molecular solids. A promising strategy is to endow the rigid lattices with controlled fluidity, wherein dynamic molecular motions can facilitate self-adjustment of reactive geometries, thereby promoting geometrically tolerant TCP. In this regard, liquid crystals (LCs), which combine the anisotropic order of crystals with the dynamic mobility of liquids, have emerged as promising candidates for developing evolutive fluid lattices [52–57]. Such a dynamically ordered molecular system is compatible with rapid molecular fluctuations such as rotation and translation while maintaining structural integrity. Consequently, reactive molecules in LC state may temporarily allow them to approach the requisite proximity to activate topochemical reactions (Fig. 1b). Meanwhile, the anisotropic organization of LC lattices can guide the reaction pathways, enabling regio- and stereo-selective transformations comparable to those observed in crystals. Thus, the dynamic control of molecular arrangements within LC-based fluid lattices offers an effective means to circumvent the stringent geometric constraints typically imposed on TCP. We have recently synthesized various columnar LCs [58,59] and achieved precise control over supramolecular polymerization process [60] and assembly architectures [61,62]. However, despite the promising potential of TCP in LCs, this effectuation has yet to be demonstrated experimentally.

To address this gap, here we report a strategy that harnesses a dynamic ordering of molecules within fluid lattices of LC phases to activate TCP beyond conventional geometric constraints, enabling high polymerization efficiency and broad monomer compatibility. Specifically, we designed a series of three-armed cyano-stilbene (CS) discotic monomers (1–6) that self-assemble into core-shell columnar LC structures. In these fluid lattices, π-stacked aromatic CS cores provide a dynamic microenvironment for directing TCP, while aliphatic shells prevent undesired intercolumnar (interchain) crosslinking (Fig. 1c). Despite the geometrical constraints of helical stacking within the columnar phases, light-activated [2 + 2] cycloaddition proceeds with near-quantitative efficiency due to the molecular adaptability inherent in the dynamic LC lattices. The one-dimensional (1D) columnar architecture promotes directional chain growth along the columnar axis, resulting in efficient TCP into linear helical polymers. These polymers exhibit dissipative behavior, undergoing spontaneous and complete depolymerization via cycloreversion to regenerate the monomers. Leveraging this dissipative property, we demonstrate that fluid-lattice-activated TCP provides an efficient approach to temporary information encryption in skin-attachable films through fluorescence visualization at body temperature, thereby offering new avenues for applications in flexible optoelectronics.