Non-innocent P-centers in nonbenzenoid polycyclic aromatic molecules with tunable structures and properties.

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Heteroatom incorporation in polycyclic aromatic molecules (PAMs) is key for tuning optoelectronic properties.
• Azulene derivatives are of interest due to their unique electronic structures.

Purpose of the Study:

• To synthesize and characterize novel nonbenzenoid polycyclic aromatic molecules (PAMs) incorporating phosphorus (P) and sulfur (S) atoms into the azulene core.
• To investigate the impact of phosphorus environments on the photophysical, electronic, and redox properties of these P-PAMs.
• To explore the potential of these P-PAMs as functional materials in optoelectronic devices.

Main Methods:

• Modular P-chemistry and cyclization reactions for synthesis of P-azulene-based PAMs.
• Photophysical studies (e.g., fluorescence, phosphorescence) and theoretical calculations.
• Electrochemical studies to analyze redox properties and radical cation formation.
• Device fabrication and testing using P-PAMs as hole-transporting layers in perovskite solar cells.

Main Results:

• Successful synthesis of the first P-azulene-based PAMs with isomeric PN- and PC-type structures.
• Demonstrated significant influence of P-environments on molecular structure and properties.
• Observed effective σ*-π* hyperconjugation in PC derivatives via P-centers.
• Reported unexpected room-temperature phosphorescence in solution for a P(iii)-centered PC derivative.
• Functionalized P-PAMs formed stable radical cations with tunable mixed-valence and open-shell characteristics.
• Achieved a 14% power conversion efficiency in perovskite solar cells using P-PAMs as hole-transporting layers.

Conclusions:

• P-PAMs represent a new class of nonbenzenoid aromatic molecules with tunable optoelectronic properties.
• The P-environment plays a crucial role in dictating the photophysical and electronic characteristics.
• These P-PAMs show promise as versatile building blocks for advanced optoelectronic applications, including solar energy conversion.