Self-Assembly of Emissive Nanocellulose/Quantum Dot Nanostructures for Chiral Fluorescent Materials

Abstract

Chiral fluorescent materials with fluorescent nanoparticles assembled into a chiral structure represent a grand challenge. Here, we report self-assembled emissive needle-like nanostructures through decorating cellulose nanocrystals (CNCs) with carbon quantum dots (CQDs). This assembly is facilitated by the heterogeneous amphiphilic interactions between natural and synthetic components. These emissive nanostructures can self-organize into chiral nematic solid-state materials with enhanced mechanical performance. The chiral CQD/CNC films demonstrate an intense iridescent appearance superimposed with enhanced luminescence that is significantly higher than that for CQD films and other reported CQD/CNC films. A characteristic fluorescent fingerprint signature is observed in the CQD/CNC film, proving the well-defined chiral organization of fluorescent nanostructures. The chiral organization of CQDs enables the solid CQD/CNC film to form a right-hand chiral fluorescence with an asymmetric factor of −0.2. Additionally, we developed chemical 2D printing and soft lithography patterning techniques to fabricate the freestanding chiral fluorescent patterns that combines mechanical intergrity and chiral nematic structure with light diffraction and emission.

Chiral Carbon Dots Synthesized on Cellulose Nanocrystals

“…The value of the g Lum at 460 nm (the wavelength corresponding to the maximum emission intensity) was 0.2, that is, significantly higher than the reported values for dye/CNC hybrids, e.g., g Lum of 3.3 × 10 −2 for pyrene/CNC hybrid obtained by Ch induction . Notably, the value of g Lum at 460 nm for C‐dot/CNC suspension was as high as some of the highest values reported for the Ch‐CNC composite films obtained from mixtures of CNCs with NPs (−0.2) or dyes (−0.28) . The origins of CPL in Ch‐CNC films and C‐dot/CNC suspension in our work is different: films effectively block L‐CPL transmission and emission, which results in R‐CPL emission with negative g Lum values, while in our work, the L‐CPL emission was stronger and g Lum was positive, due to the Ch induction or Ch nature of C‐dots themselves.…”

“…Recently, carbon nanoparticles (carbon dots, C‐dots) have been used in mixtures with CNCs to fabricate iridescent and luminescent left‐handed Ch nematic films . Control of CPL was achieved by superimposing a photoluminescence band of C‐dots and a photonic bandgap of the Ch‐CNC host, thus making composite films behave as a polarized light filter or sensor .…”

Chemical Modification of Reducing End‐Groups in Cellulose Nanocrystals

“…5–10 wt %) concentrations [33] . The propensity of CNCs to form specifically chiral nematic LCs was discovered in 1992 [34] and is still among the main lines of research on CNC‐based materials [35–38] …”

Chemische Modifizierung der reduzierenden Enden von Cellulosenanokristallen

“…[33] Diese Eigenschaft der CNCs wurde 1992 entdeckt [34] und zählt bis heute zu den Kernthemen der Forschung an CNC-basierten Materialien. [35][36][37][38] Hinsichtlich ihrer Anwendung wurden CNFs vor allem als Faserverstärkung fürK ompositmaterialien [39] oder, ohne weitere Zusätze,f ürd ie Herstellung so genannter Nanopapiere erforscht. [40] Ein weiteres,a nvisiertes Hauptanwendungsgebiet fürC NFs,v or allem im biomedizinischen Bereich, sind Hydrogel-basierte Materialien.…”

“…5–10 Gew.‐%) Konzentrationen chiral‐nematische Flüssigkristallphasen (liquid crystals, LCs) [33] . Diese Eigenschaft der CNCs wurde 1992 entdeckt [34] und zählt bis heute zu den Kernthemen der Forschung an CNC‐basierten Materialien [35–38] …”