Evolution of the electronic structure in open-shell donor-acceptor organic semiconductors

Area of Science:

• Materials Science
• Organic Electronics
• Physical Chemistry

Background:

• Organic semiconductors typically possess closed-shell electronic structures.
• Design strategies like bandgap narrowing and controlling π-system resonance can induce open-shell character.
• Understanding the transition from closed- to open-shell structures is crucial for correlating physicochemical properties with optoelectronic functionality.

Purpose of the Study:

• To investigate the molecular and electronic basis for the emergence of diradical character in donor-acceptor organic semiconductors.
• To establish structure-property relationships connecting molecular features to ground state electronic behavior.
• To demonstrate the prevalence of diradical character in commonly used organic semiconductor designs.

Main Methods:

• Synthesis of donor-acceptor organic semiconductors using diketopyrrolopyrrole and naphthobisthiadiazole acceptors with electron-rich donors.
• Characterization using Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR) spectroscopy.
• Magnetic susceptibility measurements, single-crystal X-ray diffraction, and computational investigations.

Main Results:

• Systematic demonstration of varying degrees of diradical character in synthesized donor-acceptor organic semiconductors.
• Correlation of bandgap, π-extension, structural parameters, and electronic features with the observed diradical character.
• Identification of the molecular and electronic underpinnings driving the transition to open-shell character.

Conclusions:

• Diradical character is a widespread phenomenon in classical donor-acceptor organic semiconductors.
• The study provides critical insights into the ground state structure-property relationships governing these materials.
• Findings advance the fundamental understanding of organic semiconductor electronic structures and their impact on functionality.