Perdeuterated Conjugated Polymers for Ultralow‐Frequency Magnetic Resonance of OLEDs

Abstract

The formation of excitons in OLEDs is spin dependent and can be controlled by electron‐paramagnetic resonance, affecting device resistance and electroluminescence yield. We explore electrically detected magnetic resonance in the regime of very low magnetic fields (<1 mT). A pronounced feature emerges at zero field in addition to the conventional spin‐1/2 Zeeman resonance for which the Larmor frequency matches that of the incident radiation. By comparing a conventional π‐conjugated polymer as the active material to a perdeuterated analogue, we demonstrate the interplay between the zero‐field feature and local hyperfine fields. The zero‐field peak results from a quasistatic magnetic‐field effect of the RF radiation for periods comparable to the carrier‐pair lifetime. Zeeman resonances are resolved down to 3.2 MHz, approximately twice the Larmor frequency of an electron in Earth's field. However, since reducing hyperfine fields sharpens the Zeeman peak at the cost of an increased zero‐field peak, we suggest that this result may constitute a fundamental low‐field limit of magnetic resonance in carrier‐pair‐based systems. OLEDs offer an alternative solid‐state platform to investigate the radical‐pair mechanism of magnetic‐field effects in photochemical reactions, allowing models of biological magnetoreception to be tested by measuring spin decoherence directly in the time domain by pulsed experiments.

Floquet spin states in OLEDs

“…The angle-dependence measurements of the two-photon resonance were performed in a separate low-field setup with different OLED samples, described in detail in refs. 5 , 42 . These OLEDs were much larger, with a pixel area of 3.5 mm 2 .…”

A Reductive Deuteration Approach to the Efficient Synthesis of Deuterated Polymers

“…Therefore, deuteration of polymers may improve mechanical properties, 4 decrease melting temperature, 5 alter lattice energy, 6 and/or modify conductivity. 7 For example, perdeuterated d -MEH-PPV (Scheme 1 A) was used to develop ultralow-frequency magnetic-resonance OLEDs, 1i while selectively deuterated poly(ε-caprolactone)s (PCLs, Scheme 1 B) were synthesized to achieve smaller crystal lattices and volumes. 5 However, the commercialization of deuterium-labeled polymer materials was restricted by the lack of cheap and practical synthetic approaches.…”

High-performance, low-voltage organic field-effect transistors using thieno[3,2-b]thiophene and benzothiadiazole co-polymers

“…Organic semiconducting materials have gained significant attention due to their advantages of easy processability, high mechanical flexibility, high electroactivity and chemical structure tunability in comparison with inorganic semiconductors. 13 These advantages make them promising materials in organic light emitting diodes (OLEDs), 14–17 organic solar cells, 18–20 organic photovoltaics (OPVs) 21–23 and organic field-effect transistors (OFETs). 24–30…”