Fused Rubrene Derivatives with Embedded Seven-Membered Rings: Curvature-Dependent Photophysical and Semiconductor...

Area of Science:

• Organic Chemistry
• Materials Science
• Physical Chemistry

Background:

• Rubrene is a well-known organic semiconductor with excellent charge transport properties.
• Molecular design is crucial for tuning the electronic and optical properties of organic materials.
• Incorporating fused ring systems can significantly alter molecular geometry and performance.

Purpose of the Study:

• To synthesize and characterize a novel fused rubrene derivative containing two embedded seven-membered rings.
• To investigate the conformational behavior, stability, and photophysical properties of the resulting isomers.
• To evaluate the potential of these new materials in organic electronics.

Main Methods:

• Synthesis and characterization of the fused rubrene derivative.
• Nuclear Magnetic Resonance (NMR) spectroscopy and Density Functional Theory (DFT) calculations for kinetic studies.
• Optical spectroscopy (UV-Vis, fluorescence) and transient absorption spectroscopy.
• Single-crystal X-ray diffraction and Organic Field-Effect Transistor (OFET) measurements.

Main Results:

• Two stable conformers, a C2h-symmetric saddle and a D2-symmetric twisted structure, were isolated.
• Both isomers exhibited high molecular curvature and narrower optical band gaps than non-fused rubrene.
• The saddle isomer was found to be more thermodynamically stable, with a significant isomerization barrier.
• Enhanced photostability was observed compared to parent rubrene.
• The twisted isomer demonstrated fast singlet fission, while the saddle isomer showed promising hole mobility in OFETs.

Conclusions:

• The incorporation of heptagons into the rubrene framework leads to highly curved, conformationally distinct isomers.
• These fused rubrene derivatives possess tunable optical properties and improved photostability.
• The distinct properties of the saddle and twisted isomers highlight their potential as advanced materials for organic electronics, particularly in singlet fission applications and as organic semiconductors.