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Hidden Diradical: Conformational Switch for Solvatochromic NIR Emission With Unity Quantum Yield in Thiele's
Matteo Bevilacqua1,2, Mattia Reato1, Federico Cilento3
1Dipartimento di Scienze Chimiche, Università degli Studi di Padova, Padova, Italy.
Angewandte Chemie (International Ed. in English)
|January 28, 2026
Summary
Air-stable organic diradicaloids exhibit unique photophysical properties. Conformational changes enable the design of bright luminescent materials from hidden diradicals.
Area of Science:
- Organic Chemistry
- Materials Science
- Photophysics
Background:
- Thiele-type diradicaloids are organic molecules with potential applications in materials science.
- Controlling the structure and electronic properties of diradicaloids is crucial for tuning their luminescence.
Purpose of the Study:
- To synthesize and characterize novel halogen-substituted Thiele-type diradicaloids.
- To investigate the relationship between molecular structure, conformational dynamics, and photophysical properties.
- To explore the potential of these compounds as bright luminescent materials.
Main Methods:
- Synthesis of halogen-substituted diradicaloids with varying structures.
- Photophysical characterization including UV-vis/NIR emission, photoluminescence quantum yield (PLQY), and excited-state lifetime measurements.
- Spectroscopic techniques (dual emission, transient absorption spectroscopy) and quantum chemical calculations to elucidate photophysical mechanisms.
Main Results:
- Achieved air-stable diradicaloids with folded and planar structures by manipulating halogen substituents.
- Compound 1 exhibited exceptional luminescence properties: 100% PLQY, large Stokes shift (2.0 eV), long excited-state lifetime (81 ns), and significant solvatochromism.
- Discovered that dual emission and unique photophysics of compound 1 stem from interconversion with a planar conformer (1flat) possessing high singlet diradical character and a dark doubly excited S1 state.
Conclusions:
- Conformational equilibria can be strategically employed to design highly luminescent materials.
- Hidden, air-stable organic diradicals with tunable photophysical properties can be developed.
- This work provides a pathway for creating advanced luminescent materials based on diradicaloid systems.
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