Enhancing Structural Integrity and Emission Efficiency of Two-Dimensional Supramolecular Structures Through Silica Encapsulation

The optical properties of J-aggregates are closely linked to their structural integrity, making them susceptible to chemical environments and mechanical stresses. We explore the use of silica encapsulation to enhance the structural rigidity and light emission efficiency of 5,5′,6,6′-tetrachloro-1,1′-diethyl-3,3′-di(4–sulfobutyl)-benzimidazolocarbocyanine (TDBC) two-dimensional sheet-like J-aggregates. Silica as an encapsulating matrix provides optical transparency, chemical inertness, and ease of functionalization while rigidifying the J-aggregate structure. Our novel in-situ encapsulation process results in silica-encapsulated J-aggregates whose light absorption and emission properties show no significant change from those of bare J-aggregates, indicating that encapsulation preserves the excitonic structure in TDBC J-aggregates. Microscopic analysis confirms successful and homogeneous silica coating on J-aggregate sheets through cryogenic-TEM images and Scanning Transmission Electron Microscopy with Energy Dispersive X-Ray Analysis (STEM-EDX). Dynamic Light Scattering (DLS) reveals smaller sizes for silica-coated J-aggregates compared to uncoated ones. Stability studies involving dilution demonstrate that silica coating enhances structural integrity, enabling extensive dilutions without a breakdown of J-aggregates into monomers. Silica-coated TDBC J-aggregates achieve a quantum yield of ~95%, the highest recorded for such aggregates, and an ultrafast emissive lifetime of ~200 ps. The absorbance and emission line widths, already quite narrow at room temperature, exhibit further narrowing upon cooling to 79 K. The silica shell allows attaching functional groups on the shell surface or embedding them in the silica shell, permitting hybrid systems without disturbing the assembly of J-aggregates. Encapsulated J-aggregates provide (1) a platform for further manipulation of J-aggregates as building blocks for integration with other optical materials and structures, and (2) a platform for fundamental studies of exciton delocalization, transport, and emission dynamics within a rigid matrix.<br/><br/><b>Keywords:</b> J-aggregates, silica-encapsulation, quantum yield, cyanine dyes