Electronic structure of delocalized singlet biradical Ph2-IDPL solid film

Area of Science:

• Materials Science
• Organic Electronics
• Solid-State Physics

Background:

• Diphenyl derivative of s-indacenodiphenalene (Ph(2)-IDPL) is a biradical hydrocarbon with potential applications in organic electronics.
• Previous studies indicated ambipolar field effects in amorphous Ph(2)-IDPL films.

Purpose of the Study:

• Investigate the film structure and electronic properties of Ph(2)-IDPL solid films.
• Understand the relationship between molecular structure, film morphology, and electronic properties.
• Explore the origin of the small HOMO-LUMO gap and its impact on electronic behavior.

Main Methods:

• Thin film deposition (gas-deposition method).
• Investigation of film structure and electronic structure.
• Analysis of ultraviolet photoemission spectra (UPS) with photon energy dependence.

Main Results:

• Amorphous Ph(2)-IDPL films exhibit a small highest occupied molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) gap.
• Gas-deposition enhances film crystallinity, forming quasi-one-dimensional (1D) molecular chains.
• Polycrystalline films show an extremely small HOMO-LUMO gap due to strong intermolecular coupling.
• Stacked molecular chains develop an energy band structure along the surface normal.

Conclusions:

• The small HOMO-LUMO gap is intrinsic to the singlet biradical electronic structure of Ph(2)-IDPL.
• Film crystallinity and intermolecular coupling significantly influence the electronic band structure.
• Quasi-1D energy bands form along the molecular stacking direction in polycrystalline films, driven by intermolecular covalency.