A Lego-like synthesis previously produced record-breaking nanoribbons of 30, then 53 fused rings. Now, a similar ‘accelerated’ modular methodology made a molecular nanoribbon that is triple the longest ever made – in just three simple steps. The gargantuan graphene nanoribbon is almost 36nm long, featuring 147 linearly linked rings and a conjugated core of 920 atoms. The first experiments, although preliminary, promise great applications in electronics and optoelectronics, thanks to fluorescence features that outperform state-of-the-art quantum dots.

The team, led by Aurelio Mateo-Alonso from POLYMAT in San Sebastián, Spain, developed a straightforward synthesis from smaller nanoribbons, which outperforms existing solutions in both length and precision. Different small structures just 2nm long constitute the basic building blocks, the Lego pieces – each of them has complementary terminations, with either carbonyl or amine groups. The appropriate acidic conditions trigger the click-like condensation reactions to join them together. Each iteration forms an exponentially longer nanoribbon, eventually forming the record-breaking 36nm structure.

The small sequence of steps avoids excess separations and purifications – usually a drawback of making macromolecules incrementally. The 147-ring nanoribbon is surprisingly soluble, thanks to a twisted backbone, and a substantial supply of side chains with bulky alkyl and silyl functional groups. This allows researchers to use standard synthetic chemistry techniques to purify and characterise the structure.

The nanoribbons’ solubility also simplified the study of structural, electronic and optoelectronic properties. The team notes that its nanoribbons break records in terms of fluorescence, with absorption and emission values that surpass carbon quantum dots, and competes head-to-head with the best inorganic quantum dots. This could open the door to applications in LEDs, photovoltaics, imaging and much more. Moreover, the length of the nanoribbon enabled measurements of conductivity and carrier mobility with terahertz spectroscopy, a technique that’s ineffective in smaller structures. The results, supported by DFT simulations, reveal relatively high charge mobility values, which could convey new uses in electronics.

The researchers also observed a correlation between the length of graphene nanoribbons and properties like light absorption, fluorescence and conductivity. This unprecedented understanding opens opportunities in terms of the tailored design of ultralong nanoribbons for specific applications.