Spin-Selective Photoinduced Electron Transfer within Naphthalenediimide Diradicals

Area of Science:

• Molecular Chemistry
• Quantum Information Science
• Spectroscopy

Background:

• Stable diradicals are of increasing interest for quantum information science (QIS).
• Manipulating spin states of diradicals is key for QIS applications.
• Naphthalene-1,8:4,5-bis(dicarboximide) radical anions (NDI•−) are suitable model systems.

Purpose of the Study:

• To investigate the photoinduced electron transfer dynamics of diradicals with singlet and triplet ground states.
• To understand how varying the diradical structure affects spin state populations.
• To explore the potential of photoexcitation for manipulating diradical spin states for QIS.

Main Methods:

• Time-resolved near-UV, visible, near-IR, and mid-IR spectroscopy.
• Electron Paramagnetic Resonance (EPR) spectroscopy.
• Synthesis of diradicals with varying connectivity (direct N-N linkage or benzene spacers).

Main Results:

• Singlet ground state diradicals undergo photoinduced electron transfer upon excitation, forming NDI0-NDI2−.
• Triplet ground state diradicals do not exhibit this photoinduced electron transfer.
• Spectroscopy in the 330–450 nm and 1450–1750 cm−1 ranges is crucial for distinguishing populations.
• Varying diradical connectivity alters singlet-triplet energy splitting (2J) and optical detection proportions.
• EPR spectroscopy confirmed the ground spin states.

Conclusions:

• Photoexcitation can selectively induce electron transfer in singlet diradicals but not triplet diradicals.
• The observed differences in photoresponse are critical for manipulating spin states.
• These findings have significant implications for developing photoresponsive molecular spin qubits for QIS.