Cascading Effect of Large Molecular Motion in Crystals: A Topotactic Polymorphic Transition Paves the Way to Topochemical Polymerization

Abstract

A topochemical polymerization governed by a topotactic polymorphic transition is reported. A monomer functionalized with azide and an internal alkyne crystallized as an unreactive polymorph with two molecules in the asymmetric unit. The molecules are aligned in a head-to-head fashion, thereby avoiding the azide–alkyne proximity for the topochemical azide–alkyne cycloaddition (TAAC) reaction. However, upon heating, one of the two conformers underwent a drastic 180° rotation, leading to a single-crystal-to-single-crystal (SCSC) polymorphic transition to a reactive form, wherein the molecules are head-to-tail arranged, ensuring azide–alkyne proximity. The new polymorph underwent TAAC reaction to form a trisubstituted 1,2,3-triazole-linked polymer. These results, showing unexpected topochemical reactivity of a crystal due to the intermediacy of an SCSC polymorphic transition from an unreactive form to a reactive form, highlight that predicting topochemical reactivity by relying on the static crystal structure can be misleading.

Bifurcated Polymorphic Transition and Thermochromic Fluorescence of a Molecular Crystal Involving Three-Dimensional Supramolecular Gear Rotation

“…These results not only confirm the occurrence of the 1G -to- 1Y polymorphic transition but also reveal an unusual bifurcated crystal-to-crystal polymorphic transition, leading to the simultaneous formation of both 1Y and 1G* . Given the topochemical activity of 1Y but not 1G , the 1G -to- 1Y phase transition provides a new example of stimuli-induced topochemical responses in molecular crystals. − …”

“…Stimuli-induced solid-state molecular motion and rearrangement form the basis for optical, − mechanical (morphological), − electrical, , and/or topochemical − responses of molecular crystals. A mechanistic understanding of how molecules move within the constraints of crystalline lattices and noncovalent interactions is crucial for the rational design of molecular crystals for use in machinery, sensory devices, and organic electronics.…”

Single-crystal polymers (SCPs): from 1D to 3D architectures

“…12, including the chemical structures of monomers and polymers and the transformation process in the single-crystal state. 93,95–98,151–158 In general, hydrogen-bonding interactions, such as O–H⋯O, N–H⋯O, and N–H⋯N, are the main noncovalent driving force for aligning azide and alkyne or ene-substituted derivatives in orientations suitable for their proximity-driven cycloaddition reaction in crystals. The arrangement of azide and alkyne or ene carbohydrates ( 1D-P-22 , 29 , 30 ), nucleosides ( 1D-P-23 ), and peptides ( 1D-P-24 , 25 , 26 , 27 , 28 , 31 , 32 , 33 , 34 ) have been successfully exploited for their topochemical azide–alkyne and azide-ene cycloadditions.…”

Massive Molecular Motion in Crystal Leads to an Unexpected Helical Covalent Polymer in a Solid‐state Polymerization

“…[24][25][26][27][28] There are also many topochemically reactive crystals that do not meet these criteria. [29][30][31][32][33][34][35][36] Such reactivity is due to various stimuli-induced molecular motions, within the crystal lattice, leading to the transient attainment of reactive arrangements. However, in all these cases, the molecules undergo various motions to attain a reactive orientation due to the absence of a pre-existing favorable arrangement satisfying Schmidt's criteria.…”