An extension of the CIDNP kinetics approach was proposed based on a particular example of the photoreaction between 2,2′-bipyridine (DP) and N-acetyl l-tyrosine (TyrO2−) at alkaline pH in the presence of β-cyclodextrin (CD). It was found that protonated DP radical (DPH·\documentclass[12pt]{minimal}
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\begin{document}$$DP{H^ \cdot }$$\end{document}) generated in the photoreaction is encapsulated into CD with binding constant, which is close to that for excited triplet state (3DP) and ground state (DP) of 2,2′-bipyridine and is equal to approximately 100 M− 1. The obtained T1 relaxation time of 5,5′-protons of DPH·\documentclass[12pt]{minimal}
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\begin{document}$$DP{H^ \cdot }$$\end{document} in complex with CD (8 µs) is less than in the case of free DPH·\documentclass[12pt]{minimal}
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\begin{document}$$DP{H^ \cdot }$$\end{document} (45 µs), however, it is larger than that theoretically predicted for the rigid complex (= 1.7 µs) indicating the anisotropic rotation of DPH·\documentclass[12pt]{minimal}
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\begin{document}$$DP{H^ \cdot }$$\end{document} inside CD cavity. The recombination rate constant between DPH·\documentclass[12pt]{minimal}
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\begin{document}$$DP{H^ \cdot }$$\end{document} in complex with CD and tyrosine radical (TyrO-·\documentclass[12pt]{minimal}
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\begin{document}$$Tyr{O^{ - \cdot }}$$\end{document}) (1×109M-1s-1\documentclass[12pt]{minimal}
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\begin{document}$$1 \times {10^9}\,{\text{M}^{ - 1}}\,{\text{s}^{ - 1}}$$\end{document}) is somewhat lower than the recombination rate constant between free DPH·\documentclass[12pt]{minimal}
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\begin{document}$$DP{H^ \cdot }$$\end{document} and TyrO-·\documentclass[12pt]{minimal}
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\begin{document}$$Tyr{O^{ - \cdot }}$$\end{document} (1.6×109M-1s-1\documentclass[12pt]{minimal}
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\begin{document}$$1.6 \times {10^9}\;{\text{M}^{ - 1}}\;{\text{s}^{ - 1}}$$\end{document}).
