Phenothiazine (PTZ)–anthracene (An) compact electron donor/acceptor dyads were synthesized. The molecular conformation was constrained by rotation restriction to achieve an orthogonal geometry between the electron donor (PTZ) and the electron acceptor (An), with the aim to enhance the spin–orbit charge-transfer intersystem crossing (SOCT–ISC). The substitution positions on the PTZ and An moieties were varied to attain dyads with different mutual orientations of the donor/acceptor as well as different rotation-steric hindrances. The electronic coupling strengths between the electron donor and the acceptor were quantified with the matrix elements (V DA, 0.04–0.18 eV); the smallest value was observed for the dyad with orthogonal geometry. Charge-transfer absorption and fluorescence emission bands were observed for the dyads, for which the intensity varied, manifested by the V DA values. The fluorescence of the An moiety was significantly quenched in the dyads, efficient ISC, and the formation of the triplet state were confirmed with nanosecond transient absorption spectroscopy (ΦΔ = 65%, τT = 209 μs). The rotation-steric hindrance was analyzed with potential energy curves, and PTZ was found to be an ideal electron donor to attain SOCT–ISC. Time-resolved electron paramagnetic resonance spectra revealed the electron-spin polarization (ESP) of the triplets of the dyads, which is drastically different from that of An, thus confirming the SOCT–ISC mechanism. Moreover, we found that the ESP patterns of the dyads strongly depend on the topological features of the molecules and the structure of the electron donor, thus indicating that the relationship between the molecular conformation and the ESP parameters of the triplet state of the dyads cannot be described solely by the orthogonal geometry, as was previously observed.

Time-resolved electron paramagnetic resonance (TREPR) spectroscopy is shown to be a powerful tool to characterize triplet excitons of conjugated polymers. The resulting spectra are highly sensitive to the orientation of the molecule. In thin films cast on PET film, the molecules' orientation with respect to the surface plane can be determined, providing access to sample morphology on a microscopic scale. Surprisingly, the conjugated polymer investigated here, a promising material for organic photovoltaics, exhibits ordering even in bulk samples. Orientation effects may significantly influence the efficiency of solar cells, thus rendering proper control of sample morphology highly important.

The perfluorinated dihydrophenazine derivative (perfluoro‐5,10‐bis(perfluorophenyl)‐5,10‐dihydrophenazine) (“phenazineF”) can be easily transformed to a stable and weighable radical cation salt by deelectronation (i.e. oxidation) with Ag[Al(ORF)4]/ Br2 mixtures (RF=C(CF3)3). As an innocent deelectronator it has a strong and fully reversible half‐wave potential versus Fc+/Fc in the coordinating solvent MeCN (E°′=1.21 V), but also in almost non‐coordinating oDFB (=1,2‐F2C6H4; E°′=1.29 V). It allows for the deelectronation of [FeIIICp*2]+ to [FeIV(CO)Cp*2]2+ and [FeIV(CN‐tBu)Cp*2]2+ in common laboratory solvents and is compatible with good σ‐donor ligands, such as L=trispyrazolylmethane, to generate novel [M(L)x]n+ complex salts from the respective elemental metals.

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Solution processing of conjugated polymers is key for low-cost processing of organic electronic devices. To improve solubility, introducing alkyl side chains is a commonly employed approach, known for its impact on film morphology. The morphology of polymer films is a key aspect of the structure− function relationship in organic electronic devices with a strong impact on their overall efficiency. Although planarity of conjugated backbones is advantageous for exciton and charge carrier mobilities and the overall degree of order, it leads to aggregation in solution. This reduces solubility but can result in interesting structures. Side-chain-mediated backbone torsion, in contrast, greatly enhances solubility, facilitating synthesis and control of molecular weight, but often impairs performance. Detailed insight into the impact of side chains on both morphology and electronic structure is therefore of high demand. We demonstrate time-resolved electron paramagnetic resonance spectroscopy to be perfectly suited to probe the orientation as well as the overall degree of order in conjugated polymer films, while simultaneously revealing details of the electronic structure. By systematically studying the impact of additional side chains, we distinguish their impact on the film morphology and electronic structure. Additional side chains decrease exciton delocalization but not the overall degree of order in the film. Delocalization is therefore only connected to backbone planarity. Using magnetophotoselection experiments, we additionally present clear evidence for the preferential face-on orientation of the amorphous polymer backbone on the substrate. This is crucial for the efficiency of both organic photovoltaic devices and organic light-emitting diodes.