Why Are Verdazyl Radicals Non-Emissive? An Experimental and Computational Study
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| Format: | Preprint |
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2026
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| _version_ | 1866911362542731264 |
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| author | Malinge, Alexandre Thériault, Pierre-Luc Kéna-Cohen, Stéphane |
| author_facet | Malinge, Alexandre Thériault, Pierre-Luc Kéna-Cohen, Stéphane |
| contents | Verdazyl radicals are a versatile class of air-stable organic radicals used in various applications, especially for their magnetic properties. Despite the development of a wide range of verdazyl derivatives, however, they are all non-emissive. To investigate the reasons behind this and to understand the excited-state dynamics of verdazyls, we combine steady-state and femtosecond pump-probe spectroscopy with quantum chemical calculations. In the carbazole-substituted 2,4,6-triphenylverdazyl (TPV-Cz) , we observe ultrafast internal conversion of the first excited state on a timescale of 0.5 $\pm$ 0.1 ps, followed by vibrational relaxation with a lifetime of 3.7 $\pm$ 0.4 ps. Spin-flip time-dependent density functional theory calculations reveal that the sub-picosecond non-radiative decay comes from a low-energy conical intersection between the D1 and D0 states, driven by an out-of-plane distortion of the verdazyl ring. This distortion is observed and remains energetically accessible in the isolated verdazyl ring in 2,4,6-triphenylverdazyl and in TPV-Cz. This shows that the conical intersection geometry is a recurring feature across different types of verdazyl derivatives and explains why all verdazyls are non-emissive despite different functionalization. Our results provide a mechanistic understanding of the photophysical properties of verdazyl radicals and offers a pathway for the future design of emissive verdazyl derivatives. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_05390 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Why Are Verdazyl Radicals Non-Emissive? An Experimental and Computational Study Malinge, Alexandre Thériault, Pierre-Luc Kéna-Cohen, Stéphane Chemical Physics Verdazyl radicals are a versatile class of air-stable organic radicals used in various applications, especially for their magnetic properties. Despite the development of a wide range of verdazyl derivatives, however, they are all non-emissive. To investigate the reasons behind this and to understand the excited-state dynamics of verdazyls, we combine steady-state and femtosecond pump-probe spectroscopy with quantum chemical calculations. In the carbazole-substituted 2,4,6-triphenylverdazyl (TPV-Cz) , we observe ultrafast internal conversion of the first excited state on a timescale of 0.5 $\pm$ 0.1 ps, followed by vibrational relaxation with a lifetime of 3.7 $\pm$ 0.4 ps. Spin-flip time-dependent density functional theory calculations reveal that the sub-picosecond non-radiative decay comes from a low-energy conical intersection between the D1 and D0 states, driven by an out-of-plane distortion of the verdazyl ring. This distortion is observed and remains energetically accessible in the isolated verdazyl ring in 2,4,6-triphenylverdazyl and in TPV-Cz. This shows that the conical intersection geometry is a recurring feature across different types of verdazyl derivatives and explains why all verdazyls are non-emissive despite different functionalization. Our results provide a mechanistic understanding of the photophysical properties of verdazyl radicals and offers a pathway for the future design of emissive verdazyl derivatives. |
| title | Why Are Verdazyl Radicals Non-Emissive? An Experimental and Computational Study |
| topic | Chemical Physics |
| url | https://arxiv.org/abs/2601.05390 |