Molecular-Engineered Biradicals Based on the YIII-Phthalocyanine Platform.

A mixed-ligand phthalocyanine/porphyrin yttrium(III) radical double-decker complex (DD) was synthesized using the custom-made 5,10,15-tris(4-methoxyphenyl)-20-(4-((trimethylsilyl)ethynyl)phenyl)porphyrin. The trimethylsilyl functionality was then used to couple two such complexes into biradicals through rigid tethers. Glaser coupling was used to synthesize a short-tethered biradical (C1) and Sonogashira coupling to synthesize longer-tethered ones (C2 and C3). Field-swept echo-detected (FSED), saturation recovery, and spin nutation-pulsed electron paramagnetic resonance experiments revealed marked similarities of the magnetic properties of DD with those of the parent [Y(pc)2]• complex, both in the solid state and in CD2Cl2/CDCl3 4:1 frozen glasses. FSED experiments on the biradicals C2 and C3 revealed a spectral broadening with respect to the spectra of DD and [Y(pc)2]• assigned to the effect of dipolar interactions in solution. Apart from the main resonance, satellite features were also observed, which were simulated with dipole-dipole pairs of shortest distances, suggesting spin delocalization on the organic tether. FSED experiments on C1 yielded spectral line shapes that could not be simulated as the integration of the off-resonance echoes was complicated by field-dependent modulations. While, for all dimers, the on-resonance spin nutation experiments yielded Rabi oscillations of the same frequencies, off-resonance nutations on C1 yielded Rabi oscillations that could be assigned to a MS = -1 to MS = 0 transition within a S = 1 multiplet. The DFT calculations showed that the trans conformation of the complexes was significantly more stable than the cis one and that it induced a marked spin delocalization over the rigid organic tether. This "spin leakage" was most pronounced for the shortest biradical C1.

Controlling doping efficiency in organic semiconductors by tuning short-range overscreening.

Conductivity doping has emerged as an indispensable method to overcome the inherently low conductivity of amorphous organic semiconductors, which presents a great challenge in organic electronics applications. While tuning ionization potential and electron affinity of dopant and matrix is a common approach to control the doping efficiency, many other effects also play an important role. Here, we show that the quadrupole moment of the dopant anion in conjunction with the mutual near-field host-dopant orientation have a crucial impact on the conductivity. In particular, a large positive quadrupole moment of a dopant leads to an overscreening in host-dopant integer charge transfer complexes. Exploitation of this effect may enhance the conductivity by several orders of magnitude. This finding paves the way to a computer-aided systematic and efficient design of highly conducting amorphous small molecule doped organic semiconductors.

Room-temperature spin nutations in a magnetically condensed phase of [Y(pc)2]˙.

FID-detected nutations of the antiferromagnetic crystal form of [Y(pc)2]˙ demonstrated that its radical spin can be coherently driven in its magnetically condensed undeuterated phase and at room temperature. Liquid-helium nutations revealed additional Rabi oscillations assigned to transitions within higher-multiplicity states of finite-sized chain fragments.