TY - JOUR

T1 - Magnetic-field-dependent delayed fluorescence from thermally activated reverse charge separation of spin-correlated charge separated states

AU - Groß, Tobias

AU - Mentzel, Paul

AU - Holzapfel, Marco

AU - Schmiedel, Alexander

AU - Woodward, Ben

AU - Lukzen, Nikita N.

AU - Steiner, Ulrich E.

AU - Lambert, Christoph

N1 - C. L. is grateful to the Deutsche Forschungsgemeinschaft (Project number 439533873 and IRTG2991 “Photoluminescence in Supramolecular Matrices”, Project number 517122340) N. N. L. thanks the Ministry of Science and Higher Education of the Russian Federation (126021217087-9).

PY - 2026/7/22

Y1 - 2026/7/22

N2 - Thermally activated delayed fluorescence (TADF), involving reversible electron transfer between a fluorescing S1 state and a magnetically responsive charge-separated (CS) state, constitutes a sensitive probe of the spin-chemical dynamics in the CS state as well as of the local magnetic molecular environment. With (Cl)TAA-mB-PDI and SQA-pB-PDI—featuring a Cl-substituted triarylamine ((Cl)TAA) or a squaraine unit as electron donors, meta-benzene (mB) or para-benzene (pB) bridges, and a perylene diimide (PDI) unit as electron acceptor—we introduce two novel triads with sufficiently small S1–CS energy gaps to enable TADF. Their excited state properties were investigated by femtosecond and nanosecond time-resolved transient absorption spectroscopy as well as nanosecond time-resolved fluorescence spectroscopy at variable temperatures and in variable magnetic fields. The variable temperature data were used for a full kinetic and thermodynamic characterization of the reversible electron transfer in the excited state. The magnetic-field-dependent kinetic data were thoroughly analyzed using three models of increasing complexity that explicitly include the role of the S1 state: a purely classical model, a mixed quantum – classical model, and a fully quantum-dynamical model. It is shown that the magnetic-field-dependent decay of the total CS state population is well approximated by a mono-exponential function with a magnetic-field-dependent rate constant kCSS(B). Furthermore, the delayed fluorescence proves to be a reliable indicator of the spin-dependent dynamics of the CS state. Together with two structurally related triads lacking TADF, the magnetic field effects of the new systems are placed into a broader framework that categorizes such effects using three characteristic parameters: the resonance field Bres = 2J, the resonance line width (fwhm), and the relative magnetically induced kinetic range Rk of kCSS(B). We demonstrate how these characteristic parameters depend on the kinetic properties of the systems.

AB - Thermally activated delayed fluorescence (TADF), involving reversible electron transfer between a fluorescing S1 state and a magnetically responsive charge-separated (CS) state, constitutes a sensitive probe of the spin-chemical dynamics in the CS state as well as of the local magnetic molecular environment. With (Cl)TAA-mB-PDI and SQA-pB-PDI—featuring a Cl-substituted triarylamine ((Cl)TAA) or a squaraine unit as electron donors, meta-benzene (mB) or para-benzene (pB) bridges, and a perylene diimide (PDI) unit as electron acceptor—we introduce two novel triads with sufficiently small S1–CS energy gaps to enable TADF. Their excited state properties were investigated by femtosecond and nanosecond time-resolved transient absorption spectroscopy as well as nanosecond time-resolved fluorescence spectroscopy at variable temperatures and in variable magnetic fields. The variable temperature data were used for a full kinetic and thermodynamic characterization of the reversible electron transfer in the excited state. The magnetic-field-dependent kinetic data were thoroughly analyzed using three models of increasing complexity that explicitly include the role of the S1 state: a purely classical model, a mixed quantum – classical model, and a fully quantum-dynamical model. It is shown that the magnetic-field-dependent decay of the total CS state population is well approximated by a mono-exponential function with a magnetic-field-dependent rate constant kCSS(B). Furthermore, the delayed fluorescence proves to be a reliable indicator of the spin-dependent dynamics of the CS state. Together with two structurally related triads lacking TADF, the magnetic field effects of the new systems are placed into a broader framework that categorizes such effects using three characteristic parameters: the resonance field Bres = 2J, the resonance line width (fwhm), and the relative magnetically induced kinetic range Rk of kCSS(B). We demonstrate how these characteristic parameters depend on the kinetic properties of the systems.

UR - https://www.scopus.com/pages/publications/105046022900

UR - https://www.mendeley.com/catalogue/f04bf56e-3bb1-3d88-a25e-6976c2ef4e5f/

U2 - 10.1039/d6sc02081j

DO - 10.1039/d6sc02081j

M3 - Article

C2 - 42488461

JO - Chemical Science

JF - Chemical Science

SN - 2041-6520

ER -