We have achieved an on-surface synthesis of giant conjugated macrocycles having a diameter of % 7 nm and consisting of up to 30 subunits. The synthesis started with a debrominative coupling of the molecular precursors on a hot Ag(111) surface, leading to the formation of arched oligomeric chains and macrocycles. These products were revealed by scanning tunneling microscopy in combination with density functional theory to be covalent oligomers. These intermediates also display C-Ag organometallic bonds between parallel molecular subunits due to site-selective debromination and the asymmetric molecular conformation. Subsequent cyclodehydrogenation at higher temperatures steered the final conjugation of the macrocycles. Our findings provide a novel design strategy toward p-conjugated macrocycles and open up new opportunities for the precise synthesis of organic nanostructures.
Stacking single-junction organic solar cells is effective in increasing the power conversion efficiency (PCE) by reducing the thermalization loss and increasing the open circuit voltage. Recent developments of non-fullerene acceptors (NFAs) offer a range of materials whose energy gaps are suited for absorbing relatively narrow slices of the solar spectrum, thus easing requirements for current balance between sub-elements in multijunction stacks. Here, we demonstrate a solution-processed tandem organic solar cell comprising a binary, visible-absorbing sub-cell and a ternary near-infrared (NIR) absorbing sub-cell. The ternary NIR sub-cell utilizes a narrow energy gap NFA that enables a broadened and increased absorption compared to a binary NIR sub-cell. An isopropanol surface treatment is developed to connect the hydrophilic–hydrophobic surfaces in the charge recombination zone (CRZ) located between the sub-cells. The nearly optically and electrically lossless CRZ combined with an anti-reflection coating results in tandem organic photovoltaics with PCE = 15.9% ± 0.2% under AM 1.5G simulated illumination.
Precise control over on-surface covalent reaction pathways is crucial for engineering organic nanostructures with the single-atom precision. Herein, we demonstrate a step-by-step control of an on-surface cascade covalent reaction based on a successive debromination templated by noncovalent metal− organic coordination motifs. The molecular precursor is predesigned with different reactive sites and functional ligands, allowing for both chemical and structural tuning during on-surface reactions. Through the Fe-terpyridine template effect, we are able to direct the reaction to proceed in a three-step cascade pathway and finally to achieve a porous polyarylene nanoribbon structure. The approach opens new opportunities for construction of on-surface organic nanostructures in a predictable manner.
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