Dominik Lungerich

The physicochemical properties of cationic dioxa (1), azaoxa (2), and diaza (3) [6]helicenes demonstrate a much higher chemical stability of the diaza adduct 3 (pK_R+=20.4, =−0.72 V) compared to its azaoxa 2 (pK_R+=15.2, =−0.45 V) and dioxa 1 (pK_R+=8.8, =−0.12 V) analogues. The fluorescence of these cationic chromophores is established, and ranges from the orange to the far-red regions. From 1 to 3, a bathochromic shift of the lowest energy transitions (up to 614 nm in acetonitrile) and an enhancement of the fluorescence quantum yields and lifetimes (up to 31 % and 9.8 ns, respectively, at 658 nm) are observed. The triplet quantum yields and circularly polarized luminescence are also reported. Finally, fine tuning of the optical properties of the diaza [6]helicene core is achieved through selective and orthogonal post-functionalization reactions (12 examples, compounds 4–15). The electronic absorption is modulated from the orange to the far-red spectral range (560–731 nm), and fluorescence is observed from 591 to 755 nm with enhanced quantum efficiency up to 70 % (619 nm). The influence of the peripheral auxochrome substituents is rationalized by first-principles calculations.

In rainbows: The physicochemical properties of cationic dioxa, azaoxa, and diaza [6]helicenes demonstrate remarkably high chemical stabilities, fluorescence from orange to the far-red regions with non-negligible quantum yields and lifetimes, and circularly polarized luminescence in the same ranges. Selective post-functionalization of the diaza [6]helicene introduces peripheral auxochrome substituents, the influence of which on the optical properties of the compounds is rationalized by first-principles calculations (see figure).

A meso–meso-linked diphenylamine-fused porphyrin dimer and its methoxy-substituted analogue were synthesized from a meso–meso-linked porphyrin dimer by a reaction sequence involving Ir-catalyzed β-selective borylation, iodination, meso-chlorination, and S_NAr reactions with diarylamines followed by electron-transfer-mediated intramolecular double C−H/C−I coupling. While these dimers commonly display characteristic split Soret bands and small oxidation potentials, they produced different products upon oxidation with tris(4-bromophenyl)aminium hexachloroantimonate. Namely, the diphenylamine-fused porphyrin dimer was converted into a dicationic closed-shell quinonoidal dimer, while the methoxy-substituted dimer gave a meso–meso, β-β doubly linked porphyrin dimer.

Dynamic duo: Diarylamine-fused meso–meso-linked porphyrin dimers were synthesized from a meso–meso-linked porphyrin dimer. They exhibited characteristically split Soret bands and high oxidation potentials that are due to effective perturbation by the fused diarylamine units. Depending on the peripheral substituents, oxidation of these dimers provided different products.

The electronic and molecular structures of 9,10-diamino-substituted anthracenes with different N-substituents have been re-examined. In particular, different N-substituents influence both the electronic and molecular structures of the oxidized species of 9,10-diaminoanthracenes. The anthrylene moiety of 9,10-bis(N,N-di(p-anisyl)amino)anthracene retains its planarity during the course of two successive one-electron oxidations, whereas 9,10-bis(N,N-dimethylamino)anthracene and 9,10-bis(N-p-anisyl-N-methylamino)anthracene undergo a substantial structural change to a butterfly-like structure through a two-electron oxidation process. The structural changes observed for the oxidized states are ascribed to significant differences in the frontier molecular orbitals of the above-mentioned three kinds of 9,10-diaminoanthracenes due to different extents of mixing between the amine-localized and anthrylene-localized orbitals.

Substituent effects on oxidation: 9,10-Diaminoanthracenes with N-substituents have been re-examined. Substituent variation influences electronic and molecular structures of the oxidized species (see graphic). Structural changes observed for the oxidized states may be ascribed to significant differences in the frontier molecular orbitals of 9,10-diaminoanthracenes due to mixing of amine- and anthrylene-localized orbitals.

The conversion of commercially available anilines into biaryl and biarylacetylene products was realized by using a telescoped, three-reactor flow diazotization/iododediazotization/cross-coupling process. The segmented flow stream created by off-gassing during the Sandmeyer sequence was restored to a continuous column of reaction solution by using a specially designed continuous-flow unit controlled by custom software created in-house. The resultant aryl iodide was then combined with a stream of cross-coupling solution that fed into the final reactor. The system proved versatile as modifications to the diazotization/iododediazotization sequence could be made rapidly to account for any substrate specificity (e.g., solubility problems), leading to a wide substrate scope of Suzuki–Miyaura and Sonogashira cross-coupled products.

Coupling under continuous flow: A versatile, high-yielding, flow process for the conversion of a wide variety of commercially available anilines into biaryl and biarylacetylene products is described. The system proved versatile as modifications to the diazotization/iododediazotization sequence could be made rapidly to account for any substrate specificity (e.g., solubility problems), leading to a wide substrate scope of Suzuki–Miyaura and Sonogashira cross-coupled products.