K-Y

The oxidation of closed-[7]helicenes with [bis(trifluoroacetoxy)iodo]benzene gave the corresponding dimers connected at the β-positions of the pyrrole units through a remarkably elongated C−C bond of about 1.60 Å. Homolytic bond dissociation took place upon UV irradiation to reform its monomeric form. The interconversion between monomeric and dimeric forms is associated with a turn-on of circularly polarized luminescence.

Abstract

Oxidative fusion reaction of cyclic heteroaromatic pentads consisting of pyrrole and thiophene gave closed-heterohelicene monomers and dimers depending on the oxidation conditions. Specifically, oxidation with [bis(trifluoroacetoxy)iodo]benzene (PIFA) gave closed-[7]helicene dimers connected at the β-position of one of the pyrrole units with remarkably elongated C−C bonds of about 1.60 Å. Although this bond was intact against thermal and physical activations, homolytic bond dissociation took place in DMSO upon irradiation with UV light to give the corresponding monomers. Thus, interconversion between the closed-helicene monomer and dimer was achieved. The optically pure dimer was photo-dissociated into the monomers associated with a turn-on of circularly polarized luminescence (CPL).

Nature Communications, Published online: 31 August 2023; doi:10.1038/s41467-023-41072-5

A closed-shell quinoidal backbone has been used to develop self-doped n-type conductive molecules (QnNs) with high electrical conductivities and good air stability. Intermolecular electron transfer from the amino groups to the quinoidal backbone was found to result in the self-doping. Applying the QnNs as the cathode interlayer (CIL) in organic solar cells led to an outstanding power conversion efficiency (PCE) of up to 18.2 %.

Abstract

Air stable n-type conductive molecules with high electrical conductivities and excellent device performance have important applications in organic electronics, but their synthesis remains challenging. Herein, we report three self-doped n-type conductive molecules, designated QnNs, with a closed-shell quinoidal backbone and alkyl amino chains of different lengths. The QnNs are self-doped by intermolecular electron transfer from the amino groups to the quinoidal backbone. This process is ascertained unambiguously by experiments and theoretical calculations. The use of a quinoidal structure effectively improves the self-doping level, and thus increases the electrical conductivity of self-doped n-type conductive molecules achieved by a closed-shell structure from<10⁻⁴ S cm⁻¹ to>0.03 S cm⁻¹. Furthermore, the closed-shell quinoidal structure results in good air stability of the QnNs, with half-lives>73 days; and Q4N shows an electrical conductivity of 0.019 S cm⁻¹ even after exposure to air for 120 days. When applying Q6N as the cathode interlayer in organic solar cells (OSCs), an outstanding power conversion efficiency of up to 18.2 % was obtained, which represents one the best results in binary OSCs.

Photochemistry and mechanochemistry have been combined to synthesize nanographenes in the complete absence of bulk solvents. The concept is showcased with two reactions—the Mallory reaction and the cyclodehydrochlorination, both applicable to the intramolecular formation of C−C bonds. Moreover, the approach can even form these bonds regioselectively in larger systems—something not possible before in mechanochemistry.

Abstract

Photochemical reactors inherently suffer from the low penetration depth of light and therefore rely on high dilutions to enable chemical reactions. Here we present the first method of UV (ultraviolet) photochemistry in the complete absence of bulk solvents in a ball mill. Triphenylene was synthesized by two routes, the Mallory reaction and the cyclodehydrochlorination (CDHC), resulting in yields of 81 and 92 %, respectively. The reaction was successfully scaled up to the gram scale and the robustness of the method was demonstrated for several different substrates. Finally, the regioselective assembly of nanographenes by mechanochemistry was demonstrated for larger systems. Thus, the mechanochemical approach presented here provides a powerful new tool for the atomically precise construction of nanographenes.

The synthesized macrocyclic chiral photoswitches are capable of reversible photoisomerization driven by visible light. The photoswitches show enhanced helical twisting power (HTP) in liquid crystals and diverse HTP changes upon photoisomerization. The photoswitches with shorter substituents enable visible-light-driven handedness inversion of the self-assembled helical superstructures.

Abstract

A series of macrocyclic azobenzene-based chiral photoswitches have been judiciously designed, synthesized, and characterized. In the molecular structures, binaphthyl is covalently linked to ortho-positions of azobenzene, and four different substituents are linked to 6,6′-positions of binaphthyl. The photoswitches show enhanced helical twisting power (HTP) when doping in commercially available achiral liquid crystals to form self-organized helical superstructures, i.e., cholesteric liquid crystals (CLCs). All the photoswitches exhibit reversible photoisomerization driven by visible light of different wavelengths in both organic solvent and liquid crystals. The photoswitches with shorter substituents enable handedness inversion of CLCs upon photoisomerization. These are the first examples of ortho-linked azobenzene-based photoswitches that enable handedness inversion in CLCs. The photoswitches with longer substituents display only HTP values decreasing while maintaining the same handedness.

A crystalline alkyl sidechain phase with coherence lengths >70 nm is reported in a series of representative semiconducting polymers. This ordering induces backbone disorder, revealing competing forces of the backbone and sidechain that prevent simultaneous ordering of both the constituents. Implications for molecular design that facilitates synergistic long‐range crystallization are discussed.

Abstract

Intra‐ and intermolecular ordering greatly impacts the electronic and optoelectronic properties of semiconducting polymers. The interrelationship between ordering of alkyl sidechains and conjugated backbones has yet to be fully detailed, despite much prior effort. Here, the discovery of a highly ordered alkyl sidechain phase in six representative semiconducting polymers, determined from distinct spectroscopic and diffraction signatures, is reported. The sidechain ordering exhibits unusually large coherence lengths (≥70 nm), induces torsional/twisting backbone disorder, and results in a vertically multilayered nanostructure with ordered sidechain layers alternating with disordered backbone layers. Calorimetry and in situ variable temperature scattering measurements in a model system poly{4‐(5‐(4,8‐bis(3‐butylnonyl)‐6‐methylbenzo[1,2‐b:4,5‐b′]dithiophen‐2‐yl)thiophen‐2‐yl)‐2‐(2‐butyloctyl)‐5,6‐difluoro‐7‐(5‐methylthiophen‐2‐yl)‐2H‐benzo[d][1,2,3]triazole} (PBnDT‐FTAZ) clearly delineate this competition of ordering that prevents simultaneous long‐range order of both moieties. The long‐range sidechain ordering can be exploited as a transient state to fabricate PBnDT‐FTAZ films with an atypical edge‐on texture and 2.5× improved field‐effect transistor mobility. The observed influence of ordering between the moieties implies that improved molecular design can produce synergistic rather than destructive ordering effects. Given the large sidechain coherence lengths observed, such synergistic ordering should greatly improve the coherence length of backbone ordering and thereby improve electronic and optoelectronic properties such as charge transport and exciton diffusion lengths.