Linear Dichroism Microscopy Resolves Competing Structural Models of a Synthetic Light-Harvesting Complex

Area of Science:

• Materials Science
• Photochemistry
• Nanotechnology

Background:

• Artificial light-harvesting systems are inspired by natural photosynthesis.
• Double-walled nanotubes (DWNTs) from C8S3 dye self-assemble into structures mimicking natural light-harvesting antennae.
• Two models, bricklayer (BL) and herringbone (HB), explain DWNT structure and optical properties.

Purpose of the Study:

• To resolve the debate between the bricklayer (BL) and herringbone (HB) packing models in C8S3 DWNTs.
• To elucidate the structure-property relationships governing excitonic energy transport.
• To assess the potential for engineering artificial light-harvesting complexes.

Main Methods:

• Quantum-classical simulations to determine key distinguishing parameters.
• Polarization-resolved wide-field photoluminescence microscopy.
• Experimental measurement of linear dichroism (LDr) in single DWNTs.

Main Results:

• Reduced linear dichroism (LDr) was identified as a critical parameter for model differentiation.
• Experimental LDr values up to 0.93 strongly supported the bricklayer (BL) model.
• The BL model explains superradiant exciton states and aligned transition dipoles due to negative couplings.

Conclusions:

• The bricklayer (BL) model accurately describes the structure of C8S3 DWNTs.
• Understanding excitonic coupling is key to designing efficient artificial light-harvesting systems.
• Slip-stacking engineering of DWNTs offers a pathway for tunable light-harvesting applications.