First Evidence for a Uniquely Spin‐Polarized Quartet Photoexcited State of a π‐Conjugated Spin System Generated via the Ion‐Pair State

Abstract

Ein neuartiger Spinpolarisationsmechanismus unter Beteiligung des intramolekularen Ionenpaars *A.−‐D.+‐R, der mit einem Spin‐Bahn‐Intersystem‐Crossing konkurriert, wird für die Bildung des einzigartig spinpolarisierten photoangeregten Quartettzustands von 1 vorgeschlagen. Verbindung 1 besteht aus einem bodipy‐Acceptor (A), einem Phenylanthracen‐Donor (D) und einem stabilen Verdazyl‐Radikal (R).

Intramolecular Spin Alignment within Mono‐Oxidized and Photoexcited Anthracene‐Based π Radicals as Prototypical Photomagnetic Molecular Devices: Relationships Between Electrochemical, Photophysical, and Photochemical Control Pathways

“…Photomagnetic molecular devices (PMMDs) [8] constitute the subclass of MSDs that function with light as the primary input stimulus. They potentially combine ISA with other types of intramolecular processes such as photoinduced ET and even electronic energy transfer (EnT); [64] these include specifics like enhanced and selective intersystem crossing (ISC).…”

Unique Dynamic Electron‐Spin Polarization and Spin Dynamics in the Photoexcited Quartet High‐Spin State of an Acceptor–Donor–Radical Triad

“…In our previous papers, [5] in which we used a triad system 2 with a bodipy [9] component (a well-known energy acceptor [9] for 1 D*), we reported the first evidence of a unique dynamic electron polarization in the photoexcited quartet state. Thus, in that previous work, the unique dynamic electron polarization generated by the selective populations on the highfield spin sublevels with the magnetic quantum number M S = AE 1/2 was first detected in the photoexcited quartet highspin state.…”

“…Such p-conjugated spin systems have the following advantages in the view of forthcoming organic molecular spintronics and materials science: [4,5] 1) p-Conjugated spin systems have a strong exchange coupling that leads to a robust spin alignment compared to other triplet/radical-pair systems (s-bonded systems [6] and coordination complexes [7] ). 2) In p-conjugated systems, molecules with the desired spin state can be well-designed by taking the topology of the p-electron network (p-topology) into account.…”

“…Although similar phenomena have been reported for the triplet states of the reaction centers in photosystems I and II, [10] and of their model systems, [11] this is the first observation for the quartet high-spin state. As a model of the generation of the unique dynamic electron polarization, we proposed the mechanism via a quantum-mixed charge-separated ion-pair state [5] (see details in the Supporting Information). In this model, judging from the energy location of the highest occupied molecular orbitals (HOMOs) between A and D, we assumed that the excited A moiety (A*) acts as a weak electron acceptor even in the case of bodipy.…”

“…The former unique dynamic electron polarization is explained by the following mechanism proposed previously. [5] …”