A Self‐locked β‐Cyclodextrin‐rhodamine B Spirolactam with Photoswitching Properties

• Published in: Chemistry, an Asian journal Vol. 17; no. 2; pp. e202101282 - n/a
• Main Authors: Panagiotakis, Stylianos, Saridakis, Emmanuel, Malanga, Milo, Mavridis, Irene M., Yannakopoulou, Konstantina
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 17.01.2022
• Subjects: aggregation; Aqueous solutions; Assembly; beta-Cyclodextrins; Chemistry; crystal structure; Cyclodextrins; Fluorescence; Host-guest systems; Magnetic Resonance Spectroscopy; Medical imaging; NMR; Nuclear magnetic resonance; photoswitching; Rhodamine; Rhodamine spirolactam; Rhodamines; self-assembly; Water; Zwitterions; self-assembly; NMR; crystal structure; Rhodamine spirolactam; aggregation; photoswitching; cyclodextrins; Host-guest systems
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.202101282

Supramolecular organization and self‐assembly are the pillars of functionality of many nanosystems. The covalent conjugate (6‐spirolactam rhodamine B‐6‐monodeoxy)‐β‐cyclodextrin (Rho‐βCD) is assembled as a self‐included, rigid nanostructure, identical in the crystal and in aqueous solution, as revealed by detailed X‐ray and NMR analyses. Rho‐βCD self‐assembly is the result of an interesting reaction pathway, which partially de‐aggregates Rho and disturbs the zwitterion↔spirolactone equilibrium. Rho‐βCD is stable at pH 4.6, but displays controllable photoswitching between the colored, fluorescent, zwitterionic and the colorless, non‐fluorescent closed structures, during several iterative cycles. After an initial drop in absorbance, the on‐off process continues without further changes under our irradiation conditions, a consequence of the specific self‐locked arrangement of Rho in the cavity. Rho‐βCD exemplifies a water soluble photoresponsive nanosystem with improved photostability suggesting promising applications in super resolution bioimaging. The water‐soluble spirolactam Rho‐βCD assumes a rigid, locked nanostructure both in solution and in the crystalline state that enables on‐off response to suitable light with high photostability, suggesting promising applications in bioimaging. The structure is a consequence of the supramolecular organization of Rhodamine B and 6‐monoamino‐βCD during synthesis following a distinct and unambiguous reaction pathway that is tracked in detail.