Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Review Article
  • Published:

Properties and applications of photoexcited chromophore–radical systems

Nature Reviews Chemistry volume 7, pages 75–90 (2023)Cite this article

Subjects

Abstract

Photoexcited organic chromophore–radical systems hold great promise for a range of technological applications in molecular spintronics, including quantum information technology and artificial photosynthesis. However, further development of such systems will depend on the ability to control the magnetic properties of these materials, which requires a profound understanding of the underlying excited-state dynamics. In this Review, we discuss photogenerated triplet–doublet systems and their potential to be used for applications in molecular spintronics. We outline the theoretical description of the spin system in the different coupling regimes and the invoked excited-state mechanisms governing the generation and transfer of spin polarization. The main characterization techniques used to evaluate the optical and magnetic properties of chromophore–radical systems are discussed. We conclude by giving an overview of previously investigated covalently linked triplet–radical systems, and highlight the need for further systematic investigations to improve our understanding of the magnetic interactions in such systems.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Photogenerated triplet–radical systems and their applications.
Fig. 2: Schematic illustration of the formation of trip-quartet and trip-doublet states from a radical and triplet state precursor by enhanced intersystem crossing.
Fig. 3: Illustration of the different coupling regimes.
Fig. 4: Illustration of possible excited-state processes in chromophore–radical compounds.
Fig. 5: Optical characterization of chromophore–radical systems.
Fig. 6: Identification and characterization of different spin states by transient continuous wave electron paramagnetic resonance.
Fig. 7: Pulse electron paramagnetic resonance characterization of photogenerated triplet–radical systems.
Fig. 8: Overview of investigated triplet–radical systems grouped according to different chromophore classes.

Similar content being viewed by others

References

  1. Wasielewski, M. R. et al. Exploiting chemistry and molecular systems for quantum information science. Nat. Rev. Chem. 4, 490–504 (2020). Overview of quantum information science and discussion of how chemical systems can impact quantum information science.

    Article  CAS  Google Scholar 

  2. Wolf, S. A. et al. Spintronics: a spin-based electronics vision for the future. Science 294, 1488–1495 (2001).

    Article  CAS  Google Scholar 

  3. Cornia, A. & Seneor, P. The molecular way. Nat. Mater. 16, 505–506 (2017).

    Article  CAS  Google Scholar 

  4. Moreno-Pineda, E., Martins, D. & Tuna, F. Molecules as qubits, qudits and quantum gates. Electron Paramag. Reson. 27, 146 – 187 (2021).

    Google Scholar 

  5. Atzori, M. & Sessoli, R. The second quantum revolution: role and challenges of molecular chemistry. J. Am. Chem. Soc. 141, 11339–11352 (2019).

    Article  CAS  Google Scholar 

  6. Colvin, M. T. et al. Ultrafast intersystem crossing and spin dynamics of zinc meso-tetraphenylporphyrin covalently bound to stable radicals. J. Phys. Chem. A 115, 7538–7549 (2011).

    Article  CAS  Google Scholar 

  7. Giacobbe, E. M. et al. Ultrafast intersystem crossing and spin dynamics of photoexcited perylene-3,4:9,10-bis(dicarboximide) covalently linked to a nitroxide radical at fixed distances. J. Am. Chem. Soc. 131, 3700–3712 (2009). Explanation of possible excited state deactivation processes and detailed discussion of experimental excited state dynamics.

    Article  CAS  Google Scholar 

  8. Nolden, O. et al. Excitation energy transfer and exchange-mediated quartet state formation in porphyrin-trityl systems. Chem. Eur. J. 27, 2683–2691 (2021).

    Article  CAS  Google Scholar 

  9. Mayländer, M., Chen, S., Lorenzo, E. R., Wasielewski, M. R. & Richert, S. Exploring photogenerated molecular quartet states as spin qubits and qudits. J. Am. Chem. Soc. 143, 7050–7058 (2021). First detailed pulse EPR investigation considering photogenerated quartet states in the context of quantum information science.

    Article  Google Scholar 

  10. Kandrashkin, Y. E. & van der Est, A. The triplet mechanism of electron spin polarization in moderately coupled triplet-doublet rigid complexes as a source of the enhanced +1/2 ↔ −1/2 transitions. J. Chem. Phys. 151, 184301 (2019).

    Article  Google Scholar 

  11. Kandrashkin, Y. E. & van der Est, A. Light-induced electron spin polarization in rigidly linked, strongly coupled triplet–doublet spin pairs. Chem. Phys. Lett. 379, 574–580 (2003). Perturbation theory treatment explaining the contributions of net and multiplet polarization to the spectra of strongly coupled triplet–doublet pairs.

    Article  CAS  Google Scholar 

  12. Wang, Z. et al. Efficient radical-enhanced intersystem crossing in an NDI-TEMPO dyad: photophysics, electron spin polarization, and application in photodynamic therapy. Chem. Eur. J. 24, 18663–18675 (2018).

    Article  CAS  Google Scholar 

  13. Yamauchi, S., Takahashi, K., Islam, S. S. M., Ohba, Y. & Tarasov, V. Time-resolved high-frequency EPR studies on magnesium and zinc tetraphenylporphines in their lowest excited triplet states. J. Phys. Chem. B 114, 14559–14563 (2010).

    Article  CAS  Google Scholar 

  14. Teki, Y. Excited-state dynamics of non-luminescent and luminescent π-radicals. Chem. Eur. J. 26, 980–996 (2020). Overview of different polarization-transfer mechanisms for triplet–doublet pairs.

    Article  CAS  Google Scholar 

  15. Kawai, A. & Shibuya, K. Electron spin dynamics in a pair interaction between radical and electronically-excited molecule as studied by a time-resolved ESR method. J. Photochem. Photobiol. C Photochem. Rev. 7, 89–103 (2006). Review article on weakly coupled bimolecular triplet–radical systems.

    Article  CAS  Google Scholar 

  16. Buchachenko, A. L. & Berdinsky, V. L. Electron spin catalysis. Chem. Rev. 102, 603–612 (2002).

    Article  CAS  Google Scholar 

  17. Fleck, N. et al. C–C cross-coupling reactions of trityl radicals: spin density delocalization, exchange coupling, and a spin label. J. Org. Chem. 84, 3293–3303 (2019).

    Article  CAS  Google Scholar 

  18. Wang, Z. et al. Radical-enhanced intersystem crossing in new bodipy derivatives and application for efficient triplet–triplet annihilation upconversion. J. Am. Chem. Soc. 139, 7831–7842 (2017).

    Article  CAS  Google Scholar 

  19. Han, J. et al. Doublet–triplet energy transfer-dominated photon upconversion. J. Phys. Chem. Lett. 8, 5865–5870 (2017).

    Article  CAS  Google Scholar 

  20. Nguyen, V.-N., Yan, Y., Zhao, J. & Yoon, J. Heavy-atom-free photosensitizers: from molecular design to applications in the photodynamic therapy of cancer. Acc. Chem. Res. 54, 207–220 (2021).

    Article  CAS  Google Scholar 

  21. Hattori, Y., Kusamoto, T. & Nishihara, H. Luminescence, stability, and proton response of an open-shell (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical. Angew. Chem. Int. Ed. 53, 11845–11848 (2014).

    Article  CAS  Google Scholar 

  22. Beldjoudi, Y. et al. Multifunctional dithiadiazolyl radicals: fluorescence, electroluminescence, and photoconducting behavior in pyren-1′-yl-dithiadiazolyl. J. Am. Chem. Soc. 140, 6260–6270 (2018).

    Article  CAS  Google Scholar 

  23. Ai, X. et al. Efficient radical-based light-emitting diodes with doublet emission. Nature 563, 536–540 (2018).

    Article  CAS  Google Scholar 

  24. Gaita-Ariño, A., Luis, F., Hill, S. & Coronado, E. Molecular spins for quantum computation. Nat. Chem. 11, 301–309 (2019).

    Article  Google Scholar 

  25. Troiani, F. & Affronte, M. Molecular spins for quantum information technologies. Chem. Soc. Rev. 40, 3119–3129 (2011).

    Article  CAS  Google Scholar 

  26. Rugg, B. K. et al. Photodriven quantum teleportation of an electron spin state in a covalent donor–acceptor–radical system. Nat. Chem. 11, 981–986 (2019).

    Article  CAS  Google Scholar 

  27. Olshansky, J. H., Zhang, J., Krzyaniak, M. D., Lorenzo, E. R. & Wasielewski, M. R. Selectively addressable photogenerated spin qubit pairs in DNA hairpins. J. Am. Chem. Soc. 142, 3346–3350 (2020).

    Article  CAS  Google Scholar 

  28. Ishii, K., Fujisawa, J., Ohba, Y. & Yamauchi, S. A time-resolved electron paramagnetic resonance study on the excited states of tetraphenylporphinatozinc(II) coordinated by p-pyridyl nitronyl nitroxide. J. Am. Chem. Soc. 118, 13079–13080 (1996).

    Article  CAS  Google Scholar 

  29. Ishii, K., Fujisawa, J., Adachi, A., Yamauchi, S. & Kobayashi, N. General simulations of excited quartet spectra with electron-spin polarizations: the excited multiplet states of (tetraphenylporphinato)zinc(II) coordinated by p- or m-pyridyl nitronyl nitroxides. J. Am. Chem. Soc. 120, 3152–3158 (1998).

    Article  CAS  Google Scholar 

  30. Tarasov, V. F., Islam, S. S. M., Ohba, Y., Forbes, M. D. E. & Yamauchi, S. Multifrequency TREPR investigation of excited-state ZnTPP/nitroxide radical complexes. Appl. Magn. Reson. 41, 175–193 (2011).

    Article  CAS  Google Scholar 

  31. van der Est, A., Asano-Someda, M., Ragogna, P. & Kaizu, Y. Light-induced electron spin polarization of a weakly coupled triplet–doublet spin pair in a covalently linked porphyrin dimer. J. Phys. Chem. A 106, 8531–8542 (2002). Calculated stick spectra for coupled triplet–doublet pairs in different coupling regimes.

    Article  Google Scholar 

  32. Asano, M. S., Ishizuka, K. & Kaizu, Y. Spin-multiplicity of a moderately coupled triplet–doublet spin pair in a biphenylene-linked porphyrin dimer. Mol. Phys. 104, 1609–1618 (2006).

    Article  CAS  Google Scholar 

  33. Asano, M. S., Okamura, K., Jin-mon, A., Takahashi, S. & Kaizu, Y. Enhanced intersystem crossing due to long-range exchange interaction in copper(II) porphyrin-free base porphyrin dimers: HOMO and spacer dependence. Chem. Phys. 419, 250–260 (2013).

    Article  CAS  Google Scholar 

  34. Kandrashkin, Y. E. & van der Est, A. Stimulated electron spin polarization in strongly coupled triplet–doublet spin pairs. Appl. Magn. Reson. 40, 189–204 (2011). Detailed theoretical treatment of a strongly coupled triplet–doublet spin system.

    Article  CAS  Google Scholar 

  35. Richert, S., Tait, C. E. & Timmel, C. R. Delocalisation of photoexcited triplet states probed by transient EPR and hyperfine spectroscopy. J. Magn. Reson. 280, 103–116 (2017). Review article on EPR spectroscopy of photogenerated triplet states.

    Article  CAS  Google Scholar 

  36. Kobori, Y., Fuki, M. & Murai, H. Electron spin polarization transfer to the charge-separated state from locally excited triplet configuration: theory and its application to characterization of geometry and electronic coupling in the electron donor-acceptor system. J. Phys. Chem. B 114, 14621–14630 (2010).

    Article  CAS  Google Scholar 

  37. Shushin, A. I. CIDEP in triplet–doublet quenching. Quartet–doublet nonadiabatic transitions. Z. Phys. Chem. 182, 9–18 (1993).

    Article  CAS  Google Scholar 

  38. Colvin, M. T. et al. Competitive electron transfer and enhanced intersystem crossing in photoexcited covalent TEMPO-perylene-3,4:9,10-bis(dicarboximide) dyads: unusual spin polarization resulting from the radical-triplet interaction. J. Phys. Chem. A 114, 1741–1748 (2010).

    Article  CAS  Google Scholar 

  39. Mizuochi, N., Ohba, Y. & Yamauchi, S. The structure and electronic state of photoexcited fullerene linked with a nitroxide radical based on an analysis of a two-dimensional electron paramagnetic resonance nutation spectrum. J. Chem. Phys. 111, 3479–3487 (1999). Derivation of the spin polarization starting from the triplet and doublet density matrices.

    Article  CAS  Google Scholar 

  40. van der Est, A., Kandrashkin, Y. E. & Asano, M. S. Light-induced electron spin polarization in vanadyl octaethylporphyrin: I. Characterization of the excited quartet state. J. Phys. Chem. A 110, 9607–9616 (2006).

    Article  Google Scholar 

  41. Brickmann, J. & Kothe, G. ESR of the quartet states of randomly oriented molecules: calculation of the line shape and detection of the zero-field splitting. J. Chem. Phys. 59, 2807–2814 (1973).

    Article  CAS  Google Scholar 

  42. Förster, T. Zwischenmolekulare Energiewanderung und Fluoreszenz. Ann. Phys. 437, 55–75 (1948).

    Article  Google Scholar 

  43. Skourtis, S. S., Liu, C., Antoniou, P., Virshup, A. M. & Beratan, D. N. Dexter energy transfer pathways. Proc. Natl Acad. Sci. USA 113, 8115–8120 (2016).

    Article  CAS  Google Scholar 

  44. Herbelin, S. E. & Blough, N. V. Intramolecular quenching of excited singlet states in a series of fluorescamine-derivatized nitroxides. J. Phys. Chem. B 102, 8170–8176 (1998).

    Article  CAS  Google Scholar 

  45. Green, S. A., Simpson, D. J., Zhou, G., Ho, P. S. & Blough, N. V. Intramolecular quenching of excited singlet states by stable nitroxyl radicals. J. Am. Chem. Soc. 112, 7337–7346 (1990).

    Article  CAS  Google Scholar 

  46. Ake, R. & Gouterman, M. Porphyrins XIV. Theory for the luminescent state in VO, Co, Cu complexes. Theor. Chim. Acta 15, 20–42 (1969). Theoretical foundations of EISC based on molecular orbital theory.

    Article  CAS  Google Scholar 

  47. Buchachenko, A. L. & Berdinsky, V. L. Spin catalysis of chemical reactions. J. Phys. Chem. 100, 18292–18299 (1996).

    Article  CAS  Google Scholar 

  48. Yeganeh, S., Wasielewski, M. R. & Ratner, M. A. Enhanced intersystem crossing in three-spin systems: a perturbation theory treatment. J. Am. Chem. Soc. 131, 2268–2273 (2009).

    Article  CAS  Google Scholar 

  49. Ito, A. et al. Excited-state dynamics of pentacene derivatives with stable radical substituents. Angew. Chem. Int. Ed. 53, 6715–6719 (2014).

    Article  CAS  Google Scholar 

  50. Ishii, K., Ishizaki, T. & Kobayashi, N. Experimental evidence for a selection rule of intersystem crossing to the excited quartet states: metallophthalocyanines coordinated by 4-amino-TEMPO. J. Phys. Chem. A 103, 6060–6062 (1999).

    Article  CAS  Google Scholar 

  51. Poddutoori, P. K., Kandrashkin, Y. E., Karr, P. & van der Est, A. Electron spin polarization in an Al(III) porphyrin complex with an axially bound nitroxide radical. J. Chem. Phys. 151, 204303 (2019).

    Article  Google Scholar 

  52. Franco, L. et al. TR-EPR of single and double spin-labeled C60 derivatives in frozen matrices. Appl. Magn. Reson. 30, 577–590 (2006).

    Article  CAS  Google Scholar 

  53. Dyar, S. M. et al. Photogenerated quartet state formation in a compact ring-fused perylene-nitroxide. J. Phys. Chem. B 119, 13560–13569 (2015).

    Article  CAS  Google Scholar 

  54. Poddutoori, P. K. et al. Spin–spin interactions in porphyrin-based monoverdazyl radical hybrid spin systems. Inorg. Chem. 49, 3516–3524 (2010).

    Article  CAS  Google Scholar 

  55. Kandrashkin, Y. E. & van der Est, A. Electron spin polarization of the excited quartet state of strongly coupled triplet–doublet spin systems. J. Chem. Phys. 120, 4790–4799 (2004).

    Article  CAS  Google Scholar 

  56. Teki, Y., Tamekuni, H., Takeuchi, J. & Miura, Y. First evidence for a uniquely spin-polarized quartet photoexcited state of a π-conjugated spin system generated via the ion-pair state. Angew. Chem. Int. Ed. 45, 4666–4670 (2006).

    Article  CAS  Google Scholar 

  57. Teki, Y., Tamekuni, H., Haruta, K., Takeuchi, J. & Miura, Y. Design, synthesis, and uniquely electron-spin-polarized quartet photo-excited state of a π-conjugated spin system generated via the ion-pair state. J. Mater. Chem. 18, 381–391 (2008).

    Article  CAS  Google Scholar 

  58. Takemoto, Y. & Teki, Y. Unique dynamic electron-spin polarization and spin dynamics in the photoexcited quartet high-spin state of an acceptor–donor–radical triad. ChemPhysChem 12, 104–108 (2011).

    Article  CAS  Google Scholar 

  59. Teki, Y. & Matsumoto, T. Theoretical study of dynamic electron-spin-polarization via the doublet-quartet quantum-mixed state and time-resolved ESR spectra of the quartet high-spin state. Phys. Chem. Chem. Phys. 13, 5728–5746 (2011).

    Article  CAS  Google Scholar 

  60. Mayländer, M. et al. Accessing the triplet state of perylenediimide by radical-enhanced intersystem crossing. Chem. Sci. 13, 6732–6743 (2022).

    Article  Google Scholar 

  61. Jenks, W. S. & Turro, N. J. Exchange effects and CIDEP. Res. Chem. Intermed. 13, 237–300 (1990).

    Article  CAS  Google Scholar 

  62. Rozenshtein, V. et al. Electron spin polarization of functionalized fullerenes. Reversed quartet mechanism. J. Phys. Chem. A 109, 11144–11154 (2005). Detailed discussion of spin polarization-transfer mechanisms.

    Article  CAS  Google Scholar 

  63. Gouterman, M. in The Porphyrins, Vol III (ed. Dolphin, D.) 1–165 (Academic, 1978).

  64. Maciejewski, A. et al. Transient absorption experimental set-up with femtosecond time resolution. Femto- and picosecond study of DCM molecule in cyclohexane and methanol solution. J. Mol. Struct. 555, 1–13 (2000).

    Article  CAS  Google Scholar 

  65. Megerle, U., Pugliesi, I., Schriever, C., Sailer, C. F. & Riedle, E. Sub-50 fs broadband absorption spectroscopy with tunable excitation: putting the analysis of ultrafast molecular dynamics on solid ground. Appl. Phys. B 96, 215–231 (2009).

    Article  CAS  Google Scholar 

  66. Dobryakov, A. L. et al. Femtosecond pump/supercontinuum-probe spectroscopy: optimized setup and signal analysis for single-shot spectral referencing. Rev. Sci. Instrum. 81, 113106 (2010).

    Article  CAS  Google Scholar 

  67. Lorenc, M. et al. Artifacts in femtosecond transient absorption spectroscopy. Appl. Phys. B 74, 19–27 (2002).

    Article  CAS  Google Scholar 

  68. Ruckebusch, C., Silwa, M., Pernot, P., de Juan, A. & Tauler, R. Comprehensive data analysis of femtosecond transient absorption spectra: a review. J. Photochem. Photobiol. C Photochem. Rev. 13, 1–27 (2012). Review article on the fsTA experiment with a focus on data analysis and interpretation.

    Article  CAS  Google Scholar 

  69. Devos, O., Mouton, N., Sliwa, M. & Ruckebusch, C. Baseline correction methods to deal with artifacts in femtosecond transient absorption spectroscopy. Anal. Chim. Acta 705, 64–71 (2011).

    Article  CAS  Google Scholar 

  70. Chateauneuf, J., Lusztyk, J. & Ingold, K. U. Photoinduced electron transfer from dialkyl nitroxides to halogenated solvents. J. Org. Chem. 55, 1061–1065 (1990).

    Article  CAS  Google Scholar 

  71. van Stokkum, I. H. M., Larsen, D. S. L. & van Grondelle, R. Global and target analysis of time-resolved spectra. Biochim. Biophys. Acta Bioenerg. 1657, 82–104 (2004).

    Article  Google Scholar 

  72. Beckwith, J. S., Rumble, C. A. & Vauthey, E. Data analysis in transient electronic spectroscopy–an experimentalist’s view. Int. Rev. Phys. Chem. 39, 135–216 (2020).

    Article  CAS  Google Scholar 

  73. Henry, E. R. The use of matrix methods in the modeling of spectroscopic data sets. Biophys. J. 72, 652–673 (1997).

    Article  CAS  Google Scholar 

  74. Satzger, H. & Zinth, W. Visualization of transient absorption dynamics–towards a qualitative view of complex reaction kinetics. Chem. Phys. 295, 287–295 (2003).

    Article  CAS  Google Scholar 

  75. Giurleo, J. T. & Talaga, D. S. Global fitting without a global model: regularization based on the continuity of the evolution of parameter distributions. J. Chem. Phys. 128, 114114 (2008).

    Article  Google Scholar 

  76. Torrey, H. C. Transient nutations in nuclear magnetic resonance. Phys. Rev. 76, 1059–1068 (1949).

    Article  Google Scholar 

  77. Furrer, R. et al. Transient ESR nutation signals in excited aromatic triplet states. Chem. Phys. Lett. 75, 332–339 (1980).

    Article  CAS  Google Scholar 

  78. Weber, S. Transient EPR. eMagRes 6, 255–270 (2017). Review article on the transient cw EPR method.

    Article  CAS  Google Scholar 

  79. van der Est, A. Continuous-wave EPR. eMagRes 5, 1411–1422 (2016).

    Google Scholar 

  80. Eaton, G. R., Eaton, S. S., Barr, D. P. & Weber, R. T. Quantitative EPR, 1st edn (Springer, 2010).

  81. Jeschke, G. in ESR Spectroscopy in Membrane Biophysics. Biological Magnetic Resonance, Vol. 27, 17–47 (Springer, 2007). Very informative book chapter on the practical aspects of cw and pulse EPR.

  82. Conti, F. et al. Time-resolved EPR investigation of [70]fulleropyrrolidine nitroxide isomers. Phys. Chem. Chem. Phys. 11, 495–502 (2009).

    Article  CAS  Google Scholar 

  83. Teki, Y., Miyamoto, S., Nakatsuji, M. & Miura, Y. π-topology and spin alignment utilizing the excited molecular field: observation of the excited high-spin quartet (S = 3/2) and quintet (S = 2) states on purely organic π-conjugated spin systems. J. Am. Chem. Soc. 123, 294–305 (2001).

    Article  CAS  Google Scholar 

  84. Bencini, A & Gatteschi, D. EPR of Exchange Coupled Systems (Dover, 2012).

  85. Teki, Y., Toichi, T. & Nakajima, S. π topology and spin alignment in unique photoexcited triplet and quintet states arising from four unpaired electrons of an organic spin system. Chem. Eur. J. 12, 2329–2336 (2006).

    Article  CAS  Google Scholar 

  86. Stoll, S. & Schweiger, A. EasySpin, a comprehensive software package for spectral simulation and analysis in EPR. J. Magn. Reson. 178, 42–55 (2006).

    Article  CAS  Google Scholar 

  87. Schweiger, A & Jeschke, G. Principles of Pulse Electron Paramagnetic Resonance (Oxford Univ. Press, 2001).

  88. Roessler, M. M. & Salvadori, E. Principles and applications of EPR spectroscopy in the chemical sciences. Chem. Soc. Rev. 47, 2534–2553 (2018).

    Article  CAS  Google Scholar 

  89. Stoll, S. Pulse EPR. eMagRes 6, 23–38 (2017). Review article on pulse EPR spectroscopy.

    Article  CAS  Google Scholar 

  90. Atherton, N. M. Principles of Electron Spin Resonance 1st edn (Ellis Horwood, 1993).

  91. Eaton, S. S. & Eaton, G. R. in Biomedical EPR, Part B: Methodology, Instrumentation, and Dynamics. Biological Magnetic Resonance Vol. 24/B (eds Eaton, S. R., Eaton, G. R. & Berliner, L. J.) Ch. 1, 3–18 (Springer, 2005).

  92. Cernescu, A., Maly, T. & Prisner, T. F. 2D-REFINE spectroscopy: separation of overlapping hyperfine spectra. J. Magn. Reson. 192, 78–84 (2008).

    Article  CAS  Google Scholar 

  93. Eaton, S. S. & Eaton, G. R. in Distance Measurements in Biological Systems by EPR, Biological Magnetic Resonance Vol. 19 (eds Berliner, L. J., Eaton, G. R. & Eaton, S. S.) Ch. 2, 29–154 (Springer, 2002).

  94. Eaton, S. S. & Eaton, G. R. Relaxation mechanisms. eMagRes 5, 1543–1556 (2016).

    Article  CAS  Google Scholar 

  95. Stoll, S., Jeschke, G., Willer, M. & Schweiger, A. Nutation-frequency correlated EPR spectroscopy: the PEANUT experiment. J. Magn. Reson. 130, 86–96 (1998).

    Article  CAS  Google Scholar 

  96. Astashkin, A. V. & Schweiger, A. Electron-spin transient nutation: a new approach to simplify the interpretation of ESR spectra. Chem. Phys. Lett. 174, 595–602 (1990).

    Article  CAS  Google Scholar 

  97. Mizuochi, N., Ohba, Y. & Yamauchi, S. A two-dimensional EPR nutation study on excited multiplet states of fullerene linked to a nitroxide radical. J. Phys. Chem. A 101, 5966–5968 (1997).

    Article  CAS  Google Scholar 

  98. Evans, D. F. Magnetic perturbation of the lowest triplet states of aromatic molecules by dissolved oxygen. Nature 178, 534–535 (1956).

    Article  CAS  Google Scholar 

  99. Evans, D. F. Magnetic perturbation of singlet-triplet transitions. Part II. J. Chem. Soc. 3885–3888 (1957).

  100. Hoijtink, G. J. The influence of paramagnetic molecules on singlet–triplet transitions. Mol. Phys. 3, 67–70 (1960).

    Article  CAS  Google Scholar 

  101. Hoijtink, G. J. Intermolecular electron exchange. Acc. Chem. Res. 2, 114–120 (1969).

    Article  Google Scholar 

  102. Murrell, J. N. The effect of paramagnetic molecules on the intensity of spin-forbidden absorption bands of aromatic molecules. Mol. Phys. 3, 319–329 (1960).

    Article  CAS  Google Scholar 

  103. Caldwell, R. A. & Schwerzel, R. E. Quenching of excited states by stable free radicals. Effect of di-tert-butyl nitroxide on stilbene and naphthalene triplets. J. Am. Chem. Soc. 94, 1035–1037 (1972).

    Article  CAS  Google Scholar 

  104. Green II, J. A., Singed, L. A. & Parks, J. H. Fluorescence quenching by the stable free radical di-t-butylnitroxide. J. Chem. Phys. 58, 2690–2695 (1973).

    Article  Google Scholar 

  105. Kuzmin, V. A. & Tatikolov, A. S. Formation of triplets of aromatic hydrocarbons on quenching of excited singlet states by nitroxyl radicals. Chem. Phys. Lett. 51, 45–47 (1977).

    Article  CAS  Google Scholar 

  106. Kollmar, C. & Sixl, H. Theory of a coupled doublet-triplet system: spin Hamiltonian and ESR spectra. Mol. Phys. 45, 1199–1208 (1982). Energy diagrams of coupled doublet and quartet states in different coupling regimes and for different field strengths.

    Article  CAS  Google Scholar 

  107. Blättler, C., Jent, F. & Paul, H. A novel radical-triplet pair mechanism for chemically induced electron polarization (CIDEP) of free radicals in solution. Chem. Phys. Lett. 166, 375–380 (1990).

    Article  Google Scholar 

  108. Kawai, A., Okutsu, T. & Obi, K. Spin polarization generated in the triplet–doublet interaction: hyperfine-dependent chemically induced dynamic electron polarization. J. Phys. Chem. 95, 9130–9134 (1991).

    Article  CAS  Google Scholar 

  109. Goudsmit, G.-H., Paul, H. & Shushin, A. I. Electron spin polarization in radical-triplet pairs. Size and dependence on diffusion. J. Phys. Chem. 97, 13243–13249 (1993).

    Article  CAS  Google Scholar 

  110. Fujisawa, J., Ishii, K., Ohba, Y., Iwaizumi, M. & Yamauchi, S. Electron spin polarization transfer from excited triplet porphyrins to a nitroxide radical via spin exchange mechanism. J. Phys. Chem. 99, 17082–17084 (1995).

    Article  CAS  Google Scholar 

  111. Corvaja, C., Maggini, M., Prato, M., Scorrano, G. & Venzin, M. C60 derivative covalently linked to a nitroxide radical: time-resolved EPR evidence of electron spin polarization by intramolecular radical–triplet pair interaction. J. Am. Chem. Soc. 117, 8857–8858 (1995).

    Article  CAS  Google Scholar 

  112. Liu, G., Liou, S.-H., Enkin, N., Tkach, I. & Bennati, M. Photo-induced radical polarization and liquid-state dynamic nuclear polarization using fullerene nitroxide derivatives. Phys. Chem. Chem. Phys. 19, 31823–31829 (2017).

    Article  CAS  Google Scholar 

  113. Avalos, C. E. et al. Enhanced intersystem crossing and transient electron spin polarization in a photoexcited pentacene–trityl radical. J. Phys. Chem. A 124, 6068–6075 (2020).

    Article  CAS  Google Scholar 

  114. Franco, L. et al. TR-EPR of single and double spin-labelled C60 derivatives: observation of quartet and quintet excited states in solution. Mol. Phys. 104, 1543–1550 (2006).

    Article  CAS  Google Scholar 

  115. Conti, F. et al. EPR studies on a binitroxide fullerene derivative in the ground triplet and first photoexcited quintet state. J. Phys. Chem. A 104, 4962–4967 (2000).

    Article  CAS  Google Scholar 

  116. Mizuochi, N., Ohba, Y. & Yamauchi, S. First observation of the photoexcited quintet state in fullerene linked with two nitroxide radicals. J. Phys. Chem. A 103, 7749–7752 (1999).

    Article  CAS  Google Scholar 

  117. Reginsson, G. W., Kunjir, N. C., Sigurdsson, S. T. & Schiemann, O. Trityl radicals: spin labels for nanometer-distance measurements. Chem. Eur. J. 18, 13580–13584 (2012).

    Article  CAS  Google Scholar 

  118. Bordignon, E. EPR spectroscopy of nitroxide spin probes. eMagRes 6, 235–254 (2017).

    Article  CAS  Google Scholar 

  119. Yang, Y. et al. In-cell trityl–trityl distance measurements on proteins. J. Phys. Chem. Lett. 11, 1141–1147 (2020).

    Article  CAS  Google Scholar 

  120. Toyama, N., Asano-Someda, M., Ichino, T. & Kaizu, Y. Enhanced intersystem crossing in gable-type copper(II) porphyrin-free base porphyrin dimers: evidence of through-bond exchange interaction. J. Phys. Chem. A 104, 4857–4865 (2000).

    Article  Google Scholar 

  121. Franz, M., Neese, F. & Richert, S. Calculation of exchange couplings in the electronically excited state of molecular three-spin systems. Chem. Sci. 13, 12358–12366 (2022).

    Article  CAS  Google Scholar 

  122. Moons, H. et al. W-band transient EPR and photoinduced absorption on spin-labeled fullerene derivatives. Phys. Chem. Chem. Phys. 13, 3942–3951 (2011). Well-resolved experimental spectra of triplet–radical systems, clear assignment of the transitions and experimental determination of JTR.

    Article  CAS  Google Scholar 

  123. Ito, A., Hinoshita, M., Kato, K. & Teki, Y. Excited-state dynamics and spin-exchange coupling of anthracene–verdazyl radical in frozen glass matrix investigated by transient absorption spectroscopy. Chem. Lett. 45, 1324–1326 (2016).

    Article  CAS  Google Scholar 

  124. Corvaja, C., Maggini, M., Ruzzi, M., Scorrano, G. & Toffoletti, A. Spin polarization in fullerene derivatives containing a nitroxide group. Observation of the intermediate photoexcited quartet state in radical triplet pair interaction. Appl. Magn. Reson. 12, 477–493 (1997).

    Article  Google Scholar 

  125. Mazzoni, M., Conti, F. & Corvaja, C. The sign of the exchange interaction between triplet excited fullerene and nitroxide free radicals. Appl. Magn. Reson. 18, 351–361 (2000).

    Article  CAS  Google Scholar 

  126. Poddutoori, P. K. et al. Excited state dynamics and electron transfer in a phosphorus(V) porphyrin–TEMPO conjugate. J. Chem. Sci. 133, 65 (2021).

    Article  CAS  Google Scholar 

  127. Grzegorzek, N. et al. Metalated porphyrin stable free radicals: exploration of electron spin communication and dynamics. J. Phys. Chem. A 124, 6168–6176 (2020).

    Article  CAS  Google Scholar 

  128. Ishii, K., Takeuchi, S. & Kobayashi, N. Relationship between electron spin polarization, electron exchange interaction, and lifetime: the excited multiplet states of phthalocyaninatosilicon covalently linked to one nitroxide radical. J. Phys. Chem. A 105, 6794–6799 (2001).

    Article  CAS  Google Scholar 

  129. Ishii, K., Hirose, Y., Fujitsuka, H., Ito, O. & Kobayashi, N. Time-resolved EPR, fluorescence, and transient absorption studies on phthalocyaninatosilicon covalently linked to one or two TEMPO radicals. J. Am. Chem. Soc. 123, 702–708 (2001).

    Article  CAS  Google Scholar 

  130. Takeuchi, S., Ishii, K. & Kobayashi, N. Time-resolved EPR and transient absorption studies on phthalocyaninatosilicon covalently linked to two PROXYL radicals. J. Phys. Chem. A 108, 3276–3280 (2004).

    Article  CAS  Google Scholar 

  131. Teki, Y., Miyamoto, S., Iimura, K., Nakatsuji, M. & Miura, Y. Intramolecular spin alignment utilizing the excited molecular field between the triplet (S = 1) excited state and the dangling stable radicals (S = 1/2) as studied by time-resolved electron spin resonance: observation of the excited quartet (S = 3/2) and quintet (S = 2) states on the purely organic π-conjugated spin systems. J. Am. Chem. Soc. 122, 984–985 (2000).

    Article  CAS  Google Scholar 

  132. Teki, Y. Photo-induced spin alignment utilizing the excited molecular field between the excited triplet state of phenyl- or diphenylanthracene and the dangling nitroxide radicals: theoretical investigation of the mechanism for the intramolecular spin alignment. Polyhedron 20, 1163–1168 (2001).

    Article  CAS  Google Scholar 

  133. Teki, Y., Nakatsuji, M. & Miura, Y. Excited high spin states of novel π conjugated verdazyl radicals: photoinduced spin alignment utilizing the excited molecular field. Mol. Phys. 100, 1385–1394 (2002).

    Article  CAS  Google Scholar 

  134. Mihara, N. & Teki, Y. Electronic ground state, magnetic property, and photo-excited state of ferrocene substituted phenylanthracene verdazyl radical. Inorg. Chim. Acta 361, 3891–3894 (2008).

    Article  CAS  Google Scholar 

  135. Teki, Y., Miyamoto, S. & Koide, K. π-topology and spin alignment in the photo-excited states of phenylanthracene-t-butylnitroxide radicals. Phys. Chem. Chem. Phys. 17, 31646–31652 (2015).

    Article  CAS  Google Scholar 

  136. Tamekuni, H. & Teki, Y. Design, synthesis and physical properties of the metal complexes using π-radical with photo-excited high-spin state as a ligand. Polyhedron 26, 1984–1988 (2007).

    Article  CAS  Google Scholar 

  137. Teki, Y., Kimura, M., Narimatsu, S., Ohara, K. & Mukai, K. Excited high-spin quartet (S = 3/2) state of a novel π-conjugated organic spin system, pyrene-verdazyl radical. Bull. Chem. Soc. Jpn. 77, 95–99 (2004).

    Article  CAS  Google Scholar 

  138. Imran, M. et al. Radical-enhanced intersystem crossing in perylene-oxoverdazyl radical dyads. ChemPhysChem 23, e202100912 (2022).

    Article  CAS  Google Scholar 

  139. Chernick, E. T. et al. Pentacene appended to a TEMPO stable free radical: the effect of magnetic exchange coupling on photoexcited pentacene. J. Am. Chem. Soc. 137, 857–863 (2015).

    Article  CAS  Google Scholar 

  140. Zhang, X. et al. Radical-enhanced intersystem crossing in a bay-substituted perylene bisimide–TEMPO dyad and the electron spin polarization dynamics upon photoexcitation. ChemPhysChem 22, 55–68 (2021).

    Article  Google Scholar 

  141. Jockusch, S., Dedola, G., Lem, G. & Turro, N. J. Electron spin polarization by intramolecular triplet quenching of a nitroxyl radical labeled thioxanthonedioxide. J. Phys. Chem. B 103, 9126–9129 (1999).

    Article  CAS  Google Scholar 

  142. Tripathi, A. & Rane, V. Toward achieving the theoretical limit of electron spin polarization in covalently linked radical-chromophore dyads. J. Phys. Chem. B 123, 6830–6841 (2019).

    Article  CAS  Google Scholar 

Download references

Acknowledgements

This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), project number 417643975.

Author information

Authors and Affiliations

  1. Institute of Physical Chemistry, University of Freiburg, Freiburg, Germany

    Theresia Quintes, Maximilian Mayländer & Sabine Richert

Authors
  1. Theresia Quintes
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Maximilian Mayländer
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Sabine Richert
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

T.Q., M.M. and S.R. wrote and edited the final version of this manuscript.

Corresponding author

Correspondence to Sabine Richert.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Reviews Chemistry thanks Yoshio Teki and the other anonymous reviewers for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Quintes, T., Mayländer, M. & Richert, S. Properties and applications of photoexcited chromophore–radical systems. Nat Rev Chem 7, 75–90 (2023). https://doi.org/10.1038/s41570-022-00453-y

Download citation

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41570-022-00453-y

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing