ORGS3-0271
Regulating Azobenzene Photodynamics through Cyclodextrin Cavity Size under Confinement
When and Where
Nov 30, -0001
12:00am - 12:00am
Presenter(s)
Geonwoo Lee (Ulsan National Institute of Science and Technology)
Co-Author(s)
Abstract
Supramolecular host-guest interactions are central to dynamic, stimuli-responsive materials. Cyclodextrins (CDs) selectively encapsulate guest molecules based on cavity size, while azobenzene (Azo) reversibly switches between trans and cis forms under light. Although Azo-CD complexes have been widely studied in bulk, how nanoscale confinement changes their photochemical behavior remains unclear.
Here, we investigated confinement effects on Azo-CD complexes using a Surface Forces Apparatus (SFA), which probes light-induced structural changes at confined interfaces. Confinement strongly suppressed the photodynamic response of Azo in α-CD and β-CD complexes, whereas γ-CD complexes largely retained reversible photoisomerization. This contrast indicates that CD cavity size is a decisive factor controlling Azo photoactivity under restricted geometries. It also shows why bulk measurements alone cannot fully predict molecular behavior at interfaces, where geometry becomes chemically relevant.
Spectroscopic analyses supported the SFA results. Two-dimensional ROESY NMR confirmed inclusion complex formation between Azo and all three CDs, verifying host-guest binding in each system. UV-Vis spectra showed absorption shifts in the order α-CD > β-CD > γ-CD, suggesting that smaller cavities perturb the electronic environment of Azo. These findings show that steric restriction within α-CD and β-CD limits Azo isomerization, while the larger γ-CD cavity provides enough space to preserve intrinsic light-driven dynamics.
Overall, this work demonstrates that spatial confinement is an active design parameter in supramolecular chemistry. By linking nanoscale geometry with molecular photodynamics, it provides principles for engineering light-responsive interfaces, adaptive coatings, and responsive polymers whose macroscopic properties can be programmed through confined host-guest environments.
Here, we investigated confinement effects on Azo-CD complexes using a Surface Forces Apparatus (SFA), which probes light-induced structural changes at confined interfaces. Confinement strongly suppressed the photodynamic response of Azo in α-CD and β-CD complexes, whereas γ-CD complexes largely retained reversible photoisomerization. This contrast indicates that CD cavity size is a decisive factor controlling Azo photoactivity under restricted geometries. It also shows why bulk measurements alone cannot fully predict molecular behavior at interfaces, where geometry becomes chemically relevant.
Spectroscopic analyses supported the SFA results. Two-dimensional ROESY NMR confirmed inclusion complex formation between Azo and all three CDs, verifying host-guest binding in each system. UV-Vis spectra showed absorption shifts in the order α-CD > β-CD > γ-CD, suggesting that smaller cavities perturb the electronic environment of Azo. These findings show that steric restriction within α-CD and β-CD limits Azo isomerization, while the larger γ-CD cavity provides enough space to preserve intrinsic light-driven dynamics.
Overall, this work demonstrates that spatial confinement is an active design parameter in supramolecular chemistry. By linking nanoscale geometry with molecular photodynamics, it provides principles for engineering light-responsive interfaces, adaptive coatings, and responsive polymers whose macroscopic properties can be programmed through confined host-guest environments.
