Azobenzene-Mediated Reversible Conformational Switching in 9,9′-Bifluorenylidene-Based Molecular Machines
5 affiliations
- 1Department of Chemistry
- 2University of Missouri-Saint Louis
- 3Department of Chemistry and Center for Functional Materials
- 4Wake Forest University
- 5University of Pennsylvania
Abstract
Intrinsically dynamic molecules offer attractive building blocks for molecular machines, yet controlling their conformational motion with external stimuli remains a fundamental challenge. Here, we report Azo–BF–Azo, a photoresponsive molecular machine in which an intrinsically dynamic 9,9′-bifluorenylidene (BF) core is coupled to two visible-light-responsive tetra-orthofluorinated azobenzene (Azo) units that act as molecular actuators. Irradiation at 525 nm induces trans-to-cis photoisomerization of the Azo units, accompanied by a shift of the BF framework from the closed toward the open conformation, whereas irradiation at 456 nm reverses Azo isomerization and restores the BF-closed state over time. DFT calculations reveal that the extended trans-Azo units favor intramolecular π–π interactions that stabilize the closed BF conformation, while their conversion to the folded cis state disrupts these interactions and alters the steric environment surrounding the BF core. Variable-temperature NMR spectroscopy provides experimental support for the role of these intramolecular interactions in regulating the BF conformational equilibrium. The photoinduced state additionally undergoes spontaneous thermal relaxation, recovering approximately 65% of the initial state. Together, these results demonstrate that local photoisomerization of peripheral Azo actuators can reshape the conformational landscape of an intrinsically dynamic BF core through the cooperative modulation of steric and intramolecular π–π interactions. This work provides a strategy for converting intrinsic molecular dynamics into externally programmable motion and establishes a design principle for constructing integrated molecular machines in which one type of molecular motion regulates another.
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BibTeX
@misc{mahajan2026azobenzenemediated,
title = {{Azobenzene-Mediated Reversible Conformational Switching in 9,9′-Bifluorenylidene-Based Molecular Machines}},
author = {Sohail Mahajan and Reese Rich and Lin Jiao and Duhan Zhang and Wendu Ding and Jinjia Xu and JINJIA XU},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15008803/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008803/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Azobenzene-Mediated Reversible Conformational Switching in 9,9′-Bifluorenylidene-Based Molecular Machines
AU - Sohail Mahajan
AU - Reese Rich
AU - Lin Jiao
AU - Duhan Zhang
AU - Wendu Ding
AU - Jinjia Xu
AU - JINJIA XU
PY - 2026
DA - 2026/09/14
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008803/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008803/v1
AB - Intrinsically dynamic molecules offer attractive building blocks for molecular machines, yet controlling their conformational motion with external stimuli remains a fundamental challenge. Here, we report Azo–BF–Azo, a photoresponsive molecular machine in which an intrinsically dynamic 9,9′-bifluorenylidene (BF) core is coupled to two visible-light-responsive tetra-orthofluorinated azobenzene (Azo) units that act as molecular actuators. Irradiation at 525 nm induces trans-to-cis photoisomerization of the Azo units, accompanied by a shift of the BF framework from the closed toward the open conformation, whereas irradiation at 456 nm reverses Azo isomerization and restores the BF-closed state over time. DFT calculations reveal that the extended trans-Azo units favor intramolecular π–π interactions that stabilize the closed BF conformation, while their conversion to the folded cis state disrupts these interactions and alters the steric environment surrounding the BF core. Variable-temperature NMR spectroscopy provides experimental support for the role of these intramolecular interactions in regulating the BF conformational equilibrium. The photoinduced state additionally undergoes spontaneous thermal relaxation, recovering approximately 65% of the initial state. Together, these results demonstrate that local photoisomerization of peripheral Azo actuators can reshape the conformational landscape of an intrinsically dynamic BF core through the cooperative modulation of steric and intramolecular π–π interactions. This work provides a strategy for converting intrinsic molecular dynamics into externally programmable motion and establishes a design principle for constructing integrated molecular machines in which one type of molecular motion regulates another.
ER -