Magnetic field effects on electro-photoluminescence of photoinduced electron transfer systems in a polymer film

Abstract

Magnetic field effects on photoluminescence (PL) in the presence of external electric fields have been examined for a variety of electron donor and acceptor pairs, either linked with methylene chain or randomly distributed in polymethyl methacrylate (PMMA) films, which show intermolecular photoinduced electron transfer (PIET). Application of electric fields changes the energy separation among different electronic states, because the electric dipole moment at the state under consideration is usually different from the others. The energy levels within the same spin multiplicity are also shifted or splitted by application of magnetic field. Then, simultaneous application of electric field and magnetic field induces interesting effects on PL which cannot be observed when only electric field or magnetic field is applied to molecules. In this article, experimental results of the magnetic field effect of the electric field effect both on LE fluorescence and on exciplex fluorescence resulting from PIET are presented, and the mechanism of the synergy effects of the electric and magnetic fields on PL are discussed. The hyperfine interaction of the various radical-ion pairs produced by PIET has been also determined on the basis of the synergy effects on PL, and the results are compared with the calculated values.

Rigidity and Polarity Effects on the Electronic Properties of Two Deep Blue Delayed Fluorescence Emitters

“…These quantities would be different if the molecule absorbs to an LE state but emits from a state with CT character. Such a model has been invoked to explain the behavior of some CT compounds that undergo a geometry change in the excited state that favors charge separation or that form exciplexes. − The change in dipole moment on emission of compounds in the solid state is also a measure whether the CT character of the emission transition is reduced significantly when the slow dielectric response is frozen.…”

“…Some quenching of the emission intensity due to the applied field is observed in BTZ-CBZ but not in BOX-CBZ (Figure , compare zeroth-derivative component in panels c and f). One possible cause is a field-induced change in the degree of charge separation, similar to what has been observed for exciplexes − and some conjugated materials. ,, Although it is not obvious why BTZ-CBZ would be more susceptible to this than BOX-CBZ, minimizing field-induced emission quenching is favorable for the operation of the material in OLED devices that operate under fields one or two orders of magnitude larger than those utilized here. , Overall, the emission behavior of BOX/BTZ-CBZ in the solid state is promising for mitigating unwanted emission energy shifts due to the polarity of the local environment, leading to a higher purity of the emission color in devices. Likewise, the CT character is retained in the solid state, which supports small values of Δ E ST and therefore efficient TADF.…”

Effect of an External Electric Field on the Fluorescence of a π-Conjugated Polymer Film of P3HT Sandwiched between FTO and PMMA

“…This process might be diminished on application of an electric field. Our extensive investigation of the effects of an electric field on the photoinduced electron transfer and back-electron transfer shows that these processes are affected with an electric field 21,22 as a quadratic field effect. The effects of the electric field on the rate of electron-transfer reactions originate from the change in the difference of Gibbs energies, that is, ΔG between neutral and charge-separated states on application of an electric field.…”