C-H/π-interaction-guided self-assembly in π-conjugated oligomers

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Electronics

Background:

• Oligophenylenevinylenes (OPVs) are π-conjugated molecules with potential applications in organic electronics.
• Understanding self-assembly mechanisms is crucial for controlling the properties of organic materials.
• CH/π interactions, a non-covalent force, play a significant role in molecular recognition and self-assembly.

Purpose of the Study:

• To investigate CH/π hydrogen-bond-driven self-assembly in π-conjugated OPVs.
• To elucidate the molecular-level origins of these interactions using single-crystal structures.
• To explore the influence of CH/π interactions on the thermotropic liquid crystallinity and photophysical properties of OPVs.

Main Methods:

• Synthesis of OPVs with varying hydrocarbon or fluorocarbon tails.
• Single-crystal X-ray diffraction to analyze molecular packing and interactions.
• Thermotropic liquid crystallinity studies.
• Photophysical measurements, including time-resolved fluorescence decay.

Main Results:

• Direct evidence of CH/π interactions between π-rings and alkyl C-H groups in hydrocarbon OPVs.
• CH/π interactions promote close-packing and lamellar structures, leading to distinct liquid crystalline phases (nematic, smectic A, smectic C).
• Hydrocarbon and fluorocarbon OPVs exhibit different molecular arrangements (J-type and H-type, respectively) influencing their emission colors (yellowish/green and blue) and fluorescence lifetimes.

Conclusions:

• CH/π interactions are a primary driving force for self-assembly in OPVs, dictating their liquid crystalline behavior and solid-state packing.
• The nature of the molecular tails (hydrocarbon vs. fluorocarbon) significantly impacts self-assembly, phase behavior, and photoluminescence.
• Tailoring CH/π interactions offers a pathway to control the self-assembly and optoelectronic properties of π-conjugated materials.