This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Self-assembling, anthracene-based supramolecular nanofibers can enable excitons to migrate hundreds of nanometers, according to a new experimental finding by researchers at Science Tokyo. Coupling these nanofibers with a plasmonic gold nanohole substrate further doubles exciton diffusivity.
By mitigating the limited diffusivity of singlet excitons in organic semiconductors, this approach offers a new strategy for improving optoelectronic technologies. For decades, one of the biggest challenges in organic optoelectronics has been the limited diffusivity of excitons. Created when light is absorbed, excitons diffuse through the semiconducting material before they can dissociate into free charge carriers to generate electricity.
However, excitons in conventional organic semiconductors typically diffuse only up to 5–20 nm before recombining, limiting the performance of optoelectronic devices. Now, researchers from the Institute of Science Tokyo (Science Tokyo) in Japan have managed to overcome this long-standing limitation by combining molecular self-assembly with plasmonic nanotechnology. The breakthrough comes from a study conducted by a collaborative research team comprising Professor Martin Vacha and Associate Professor Yoshimitsu Sagara from Science Tokyo and Dr.
Takatoshi Fujita from the National Institute for Quantum Science and Technology in Japan. The findings are published in the journal Nano Letters. "Developing a universal design principle for long-range exciton transport has remained an elusive goal, necessitating a deeper comprehension of intrinsic molecular factors to strategically enhance migration within organic systems," explains Vacha.
The team designed molecules based on 9,10-bis(phenylethynyl)anthracene (BPEA) and modified the BPEA chromophore with amide groups to promote self-assembly through hydrogen bonding. These interactions organize the molecules into highly ordered one-dimensional nanofibers, while hydrophilic dendritic side chains ensured sufficient solubility. The molecular arrangement forms what are known as "J-aggregates," ordered assemblies known to facilitate efficient electronic coupling and energy transport.
The researchers combined confocal fluorescence microscopy with position-dependent fluorescence lifetime measurements to assess exciton migration. By tracking how fluorescence broadened over time after laser excitation, they found that excitons traveled remarkably long distances along the nanofibers. The nanofibers exhibited transport lengths of up to 350 nm and diffusion coefficients reaching up to 0.7 cm²/s, which rank among the highest reported for organic solids.
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