Calcium Carbonate as an Ionic Molecular Lock for Ultrastrong Fluorescence of Single Organic Molecules

Locking molecular conformation are widely applied in molecular engineering for improved performance. However, locking via organic functional groups often changes the original molecular properties. Following the rigidity and stability of ionic interaction in ionic compounds, we suggested the use of a molecular-scale ionic compound, calcium carbonate oligomer, as a robust molecular segment to functionalize organic molecules. The rigid structure of the ionic molecular segments locked the organic molecules, which could remarkably limit the intramolecular motion and intermolecular interactions. This ensured a stable and ultrastrong fluorescence of the single organic molecule while preserving its original maximum emission wavelength. The locking strategy was general and extendable to multiple organic molecules. Additionally, the ultrastrong single-molecular fluorescence can be maintained in inorganic solids with even higher quantum yields and almost unchanged maximum emission wavelength. The highest quantum yield of the investigated molecules reached 99.9 %, superior to all reported organic-inorganic fluorescent composite under air conditions. This work demonstrates a general strategy to restrict intramolecular motion and intermolecular interactions by using ionic oligomers as molecular locks, providing an alternative method for realizing ultraemissive molecules. This further demonstrates a fascinating example of molecular engineering in the presence of inorganic ionic molecules.