Related Experiment Video
Updated: Aug 6, 2026
Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity
Published on: March 6, 2017
Magnetic-field-dependent delayed fluorescence from thermally activated reverse charge separation of spin-correlated
Tobias Groß1, Paul Mentzel1, Marco Holzapfel1
1Institut für Organische Chemie, Julius-Maximilians-Universität Würzburg Am Hubland Würzburg 97074 Germany christoph.lambert@uni-wuerzburg.de.
Abstract:
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 k CSS(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 B res = 2J, the resonance line width (fwhm), and the relative magnetically induced kinetic range R k of k CSS(B). We demonstrate how these characteristic parameters depend on the kinetic properties of the systems.
Related Concept Videos
01:23Atomic Nuclei: Nuclear Relaxation Processes
01:03Atomic Nuclei: Nuclear Spin State Overview
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
01:05Atomic Nuclei: Magnetic Resonance
01:14Atomic Nuclei: Nuclear Spin State Population Distribution
01:25Magnetic Field due to Moving Charges
Consider a point charge moving with a constant velocity. Like the electric field, the magnetic field at any point is directly proportional to the magnitude of the charge and inversely proportional to the square of the distance between the source point and the field point. However, unlike the electric field, the magnetic field is always perpendicular to the plane containing the line...