title: Multi-responsive cellulose nanocrystal-rhodamine conjugates: an advanced structure study by solid-state dynamic nuclear polarization (DNP) NMR.
abstract: Multi-stimuli responsive materials based on cellulose nanocrystals (CNCs), especially using non-conventional stimuli including light, still need more explorations, to fulfill the requirements of complicated application environments. The structure determination of functional groups on the CNC surface constitutes a significant challenge, partially due to their low amounts. In this study, rhodamine spiroamide groups are immobilized onto the surface of CNCs leading to a hybrid compound being responsive to pH-values, heat and UV light. After the treatment with external stimuli, the fluorescent and correlated optical color change can be induced, which refers to a ring opening and closing process. Amine and amide groups in rhodamine spiroamide play the critical role in this switching process. Solid-state NMR spectroscopy coupled with sensitivity-enhanced dynamic nuclear polarization (DNP) was used to measure (13)C and (15)N in natural abundance, allowing the determination of structural changes during the switching process. It is shown that a temporary bond through an electrostatic interaction could be formed within the confined environment on the CNC surface during the heat treatment. The carboxyl groups on the CNC surface play a pivotal role in stabilizing the open status of rhodamine spiroamide groups.
authors.affiliation: Eduard-Zintl-Institute for Inorganic Chemistry and Physical Chemistry, Technical University Darmstadt, Alarich-Weiss-Str. 4, D-64287 Darmstadt, Germany. gutmann@chemie.tu-darmstadt.de.
authors.forename: Li
authors.initials: L
authors.lastname: Zhao
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Andreas
authors.initials: A
authors.lastname: Plog
authors.forename: Yeping
authors.initials: Y
authors.lastname: Xu
authors.forename: Gerd
authors.initials: G
authors.lastname: Buntkowsky
authors.forename: Torsten
authors.initials: T
authors.lastname: Gutmann
authors.forename: Kai
authors.initials: K
authors.lastname: Zhang