Radical-enhanced intersystem crossing, spin dipolar interaction and electron exchange in perylenebisimide-TEMPO dyads

Year: 2025

Authors: Li Z.J., Sukhanov A.A., Ito T., Sambucari G., Chen X., Bussotti L., Zhao J.Z., Voronkova V.K., Di Donato M., Kurashige Y.

Autors Affiliation: Dalian Univ Technol, Frontier Sci Ctr Smart Mat, Sch Chem Engn, State Key Lab Fine Chem, E 208 West Campus,2 Ling Gong Rd, Dalian 116024, Peoples R China; RAS, Zavoisky Phys Tech Inst, FRC Kazan Sci Ctr, Sibirsky Tract 10-7, Kazan 420029, Russia; LENS European Lab Nonlinear Spect, Via N Carrara 1, I-50019 Florence, Italy; ICCOM CNR, Via Madonna Piano 10, I-50019 Sesto Fiorentino, FI, Italy; Kyoto Univ, Grad Sch Sci, Dept Chem, Kitashirakawa Oiwake Cho,Sakyo Ku, Kyoto, Japan; CNR INO, Largo Enrico Fermi 6, I-50125 Florence, FI, Italy.

Abstract: 4-Amino-2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radical was linked to perylene-3,4:9,10-bis(dicarboximide) (PBI) at varying distances and orientations. PBI-TEMPO dyads with the radical linked at the bay-position show a charge transfer absorption band in the UV-vis absorption spectra. With increasing solvent polarity, a fluorescence quenching is observed for these dyads, whereas for a derivative with TEMPO attached at the imide-position, such polarity dependency for fluorescence spectra was not observed. Steady state and femtosecond/nanosecond time-resolved optical spectroscopy confirmed the occurrence of radical-enhanced intersystem crossing (REISC. k(ISC) = (23 ps)(-1) – (0.5 ns)(-1)). The lifetime of the (PBI)-P-3* state (tau(T) = 1.0-7.6 mu s) depends on the distance and orientations between TEMPO and PBI units. The results indicate that stronger electron spin-spin dipolar interaction (v(dd)) between the radical and the chromophore improve REISC efficiency. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy demonstrates different electron exchange interactions (J(TR)) in the dyads, varying from ferromagnetic interaction corresponding to strong exchange regime to weak antiferromagnetic exchange interaction with increasing the distance between PBI and TEMPO units. Transient-nutation experiments further clarify the TREPR signals. DFT calculations indicate that changes in the dyad structure alter the exchange coupling from ferromagnetic (J(TR) = 0.47 cm(-1)) to antiferromagnetic (J(TR) = -0.03 cm(-1) and -0.01 cm(-1)).

Journal/Review: PURE AND APPLIED CHEMISTRY

More Information: J.Z. thanks the NSFC (22473021 and U2001222), the National Key Research and Development Program of China (the Ministry of Science and Technology, No. 2023YFE0197600), the Research and Innovation Team Project of Dalian University of Technology (DUT2022TB10), the Fundamental Research Funds for the Central Universities (DUT22LAB610) and the State Key Laboratory of Fine Chemicals for financial support. A.A.S. and V.K.V. acknowledge financial support from the government assignment for FRC Kazan Scientific Centre of RAS. M.D.D. thanks the European Union’s Horizon 2020 research and innovation program under grant agreement NO. 871124 Laser lab-Europe for the support.
KeyWords: distances and orientations; electron exchange interactions; electron spin-spin dipolar interaction; exchange regime; ICPOC-26; radical-enhanced intersystem crossing
DOI: 10.1515/pac-2025-0487