Continuous Control of Thermal Responses in Dynamic Crystals via Solid Solution Engineering

Abstract

Dynamic responses in molecular crystals offer unique opportunities for creating adaptive and functional materials. Achieving precise and continuous control over these behaviors, however, remains a central challenge due to their complex phase transition mechanisms. In this work, we construct full-range solid solutions by thermally responsive penciclovir with its analogue ganciclovir. By systematically increasing ganciclovir content, the dynamic responses undergo a qualitative evolution, shifting from symmetry breaking based bending to rare cracking-healing behavior, and eventually to complete suppression. Notably, this shift is accompanied by a substantial 120 K elevation in transition temperature. Structural and thermal expansion analyses reveal that while the crystal packing remains intact, the shift in responsiveness originates from a fundamental change in the phase transition mechanism. Ganciclovir incorporation precisely modulates intermolecular interactions, increasing the transition energy barrier and suppressing symmetry breaking. Compared to simple transition temperature tuning, the switching of response types offers broader functional applicability. This work establishes a robust structure-property relationship and provides general design principles for modulating dynamic behaviors in advanced smart materials.