Excited-State Carrier Dynamics in Semiconducting Heterostructures from Self-Sorted NIR Active Dyes

Area of Science:

• Materials Science
• Organic Electronics
• Supramolecular Chemistry

Background:

• Heterostructures are crucial for organic electronics, but achieving controlled self-assembly remains a challenge.
• Self-sorting in heterostructures can improve exciton diffusion and charge separation, vital for device efficiency.
• Macrocyclic molecules, unlike small organic molecules, have not been extensively studied for self-sorting due to assembly complexities.

Purpose of the Study:

• To investigate the self-assembly behavior of novel near-infrared (NIR) active D-π-D and A-π-A porphyrin-appended molecules.
• To explore molecular-level self-sorting in mixtures of these molecules and its impact on nanostructure formation.
• To evaluate the electronic properties, particularly electrical conductivity, of the resulting self-sorted heterostructures.

Main Methods:

• Synthesis of two NIR-active molecules: a D-π-D (1) and an A-π-A (2) type.
• Characterization of self-assembled nanostructures (0D and 2D) formed by individual molecules and their mixtures.
• Analysis of self-sorted core-shell heterostructures using π-π stacking interactions.
• Spectroscopic techniques (femtosecond-transient absorption) and electrochemical methods (impedance spectroscopy) to confirm electron transfer and conductivity.

Main Results:

• Individual molecules self-assembled into J-aggregate based 0D and 2D nanostructures.
• Mixtures of molecules 1 and 2 exhibited molecular-level self-sorting, forming nanospheres and sheets that further assembled into core-shell heterostructures.
• Electrical conductivity of the self-sorted heterostructures was 10 times higher than individual assemblies.
• Excited-state electron transfer from the D-π-D molecule to the A-π-A molecule was confirmed in the mixture.

Conclusions:

• Controlling self-sorted heterostructures at the molecular level is a viable strategy for enhancing electronic properties.
• The developed NIR-active molecules and their self-sorted assemblies show promise for applications in organic solar cells (OSCs).
• This work opens new avenues for designing advanced organic electronic materials through tailored supramolecular assembly.