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

Abstract

The ability of molecules to move and rearrange in the solid state accounts for the polymorphic transition and stimuliresponsive properties of molecular crystals. However, how the crystal structure determines the molecular motion ability remains poorly understood. Here, we report that a three-dimensional (3D) supramolecular gear network in the green-emissive polymorph 1G of a dialkylamino-substituted anthracene-pentiptycene π-system (1) enables an unusual bifurcated polymorphic transition into a yellow-emissive polymorph (1Y) and a new green-emissive polymorph (1G*) via 3D correlated supramolecular rotation. The 90°forward correlated rotation causes the molecular conformation between the octyl and the anthracene units to change from syn to anti, the ladder-like supramolecular columns to constrict, and the gear network to disengage. This cooperative molecular motion is marked by the gradual formation of an intermediate state (1I) across the entire crystal from 170 to 230 °C, which then undergoes bifurcated (forward or backward rotation) and irreversible transitions to form polymorphs 1Y and 1G* at 230−235 °C. Notably, 1G* is similar to 1G but lacks gear engagement, preventing its transformation into 1Y. Nevertheless, 1G can be restored by grinding 1Y or 1G* or fuming with dichloromethane (DCM) vapor. This work illustrates the correlation between the crystal structure and solid-state molecular motion behavior and demonstrates how a 3D molecular gear system efficiently transmits thermal energy to drive the polymorphic transition and induce fluorochromism through significant conformational and packing changes.

Fabrication of efficient and red-emissive salicylaldehyde Schiff base isomers for multi-scenario information decryption

“…Stimuli-responsive fluorescent materials (SRFMs) are smart materials that can alter fluorescence signals in response to external stimuli, including light, 1,2 mechanical force, 3–5 temperature, 6,7 and pH. 8–10 Due to their vast potential applications in anti-counterfeiting, 11,12 information encryption–decryption, 13,14 biochemical sensors, 15–18 and optoelectronic devices, 19,20 the development of SRFMs has gained significant attention in recent years.…”

One-Pot Synthesis of Bis(arylamino)pentiptycenes by TiCl4-DABCO Assisted Reductive Amination of Pentiptycene Quinone

“…Pentiptycene possesses a rigid H-shaped scaffold, which has found wide utility in supramolecular chemistry and materials chemistry, − such as fluorescent sensors, − molecular devices, ,, host–guest systems, , macrocycles, porous materials, − dynamic crystals, , and redox-active polymers. , The majority of these applications require substitutions on the central phenylene ring of pentiptycene. While the readily prepared pentiptycene quinone ( 1 ) serves as an ideal precursor for this purpose, , some of the derivatization of 1 toward the designated materials suffer from multistep synthesis and low overall yields.…”

“…Pentiptycene possesses a rigid H-shaped scaffold, which has found wide utility in supramolecular chemistry and materials chemistry, 1 − 14 such as fluorescent sensors, 1 − 3 molecular devices, 1 , 2 , 4 host–guest systems, 5 , 6 macrocycles, 7 porous materials, 8 − 10 dynamic crystals, 11 , 12 and redox-active polymers. 13 , 14 The majority of these applications require substitutions on the central phenylene ring of pentiptycene.…”