A new class of fully conjugated indenofluorenes has been synthesized and confirmed by solid-state structure analysis. These indeno[2,1-c]fluorene molecules, containing an antiaromatic as-indacene core (in red), possess high electron affinities and show a broad absorption that reaches into the near-IR region of the electromagnetic spectrum. All of the featured compounds reversibly accept up to two electrons. Their electronic properties make this class of compounds attractive for applications in organic electronic devices.

The synthesis and characterization of a series of quinoidal diindeno(thieno)thiophenes (DI[n]Ts) are reported. NIR absorption, deep LUMO energy levels and progressively tighter solid-state packing allude to organic materials applications.

The synthesis and characterization of four fully-conjugated indacenedithiophenes (IDTs) are disclosed. In contrast to anthradithiophenes, regioselective synthesis of both syn and anti isomers is readily achieved. Thiophene fusion imparts increased paratropic character on the central indacene core as predicted by DFT calculations and confirmed by 1H NMR spectroscopy. IDTs exhibit red-shifted absorbance maxima with respect to their all-carbon analogues and undergo two-electron reduction and one-electron oxidation.

The synthesis and optoelectronic properties of 24 π-electron, formally antiaromatic 4,11-di-t-butyl-1,8-dimesitylfluoreno[4,3-c]fluorene (FF) are presented. The solid-state structure shows that the outer rings are aromatic, while the central four rings possess a bond-localized 2,6-naphthoquinone dimethide motif (in red). The biradical character of FF is assessed experimentally and computationally; the results of which implicate a closed-shell ground state.

The aryl–ethynyl linkage has been extensively employed in the construction of hosts for a variety of guests. Uses range from ion detection (e.g., of metal cations in the environment or industrial waste and of anions prevalent in nature), to molecular mimics for biological systems, and to applications targeting future safety issues (such as CO2 capture and indicators for the manufacture of chemical weapons). This Focus Review examines the utilization of the aryl–ethynyl linkage in engineering host molecules for a variety of different guests, and how the alkyne unit plays an integral part as both a rigid scaffolding section in host geometry design as well as a linker to allow conjugative communication between discrete π-electron systems.

Treatment of 2-ethynylanilines with P(OPh)3 gives either 2,2-diphenoxy-2-λ5-phosphaquinolines or 2-phenoxy-2-λ5-phospha-quinolin-2-ones under transition metal-free conditions. This reaction offers unparalleled access to an underexplored heterocycle, which opens study of the fundamental nature of the N=PV double bond and its potential for delocalization within a cyclic π-electron system. This heterocycle can inherently serve as a carbostyril mimic, with application as a bioisostere for pharmaceuticals based on the 2-quinolone scaffold. Additionally, the molecule holds promise as a new fluorophore, as initial screening reveals quantum yields upwards of ~40%, Stokes shifts of 50–150 nm, and emission wavelengths of 380–540 nm. The phosphaquinolin-2-ones possess one of the strongest solution-state dimerization constants for a D-A system (130 M−1) due to the close proximity of a strong acceptor, P=O, and a strong donor, the phosphonamidate N–H, suggesting this class of compounds might hold promise as new hydrogen bonding hosts for optoelectronic sensing of anions and/or small molecules.

SummaryWe report a new synthetic route to 5,11-disubstituted indeno[1,2-b]fluorene-6,12-diones that is amenable to larger scale reactions, allowing for the preparation of gram amounts of material. With this new methodology, we explored the effects on crystal packing morphology for the indeno[1,2-b]fluorene-6,12-diones by varying the substituents on the silylethynyl groups.

The synthesis and characterization of indacenediselenophene (IDS) and diindenoselenophene (DIS), the selenophene-containing analogues of indacenedithiophene (IDT) and diindenothiophene (DIT), respectively, are described. Cyclic voltammetry reveals that IDS and DIS both undergo a two-electron reduction and a one-electron oxidation and have narrower HOMO/LUMO energy gaps when compared to their thiophene-containing counterparts. The UV-Vis spectrum of IDS exhibits a red-shifted absorbance maximum with respect to the Scontaining IDT, and single crystal XRD shows close C-Se contacts of 3.407 Å (IDS) and close CC contacts of 3.358 Å (DIS).