Inclusion of quinoidal cores in conjugated hydrocarbons is a common strategy to modulate the properties of diradicaloids formed by aromaticity recovery within the quinoidal unit. Here we describe an alternative approach of tuning of diradical properties in indenoindeno­dibenzo­thiophenes upon anti → syn isomerism of the benzothiophene motif. This alters the relationship of the S atom with the radical center from linear to cross conjugation yet retains the same 2,6-naphtho conjugation pattern of the rearomatized core. We conduct a full comparison between the anti and syn derivatives based on structural, spectroscopic, theoretical, and magnetic measurements, showing that these systems are stable open-shell singlet diradicaloids that only access their triplet state at elevated temperatures.

The preparation of a series of dibenzo- and tetrabenzo-fused fluoreno­[3,2-b]­fluorenes is disclosed, and the diradicaloid properties of these molecules are compared with those of a similar, previously reported series of anthracene-based diradicaloids. Insights on the diradical mode of delocalization tuning by constitutional isomerism of the external naphthalenes has been explored by means of the physical approach (dissection of the electronic properties in terms of electronic repulsion and transfer integral) of diradicals. This study has also been extended to the redox species of the two series of compounds and found that the radical cations have the same stabilization mode by delocalization that the neutral diradicals while the radical anions, contrarily, are stabilized by aromatization of the central core. The synthesis of the fluorenofluorene series and their characterization by electronic absorption and vibrational Raman spectroscopies, X-ray diffraction, SQUID measurements, electrochemistry, in situ UV–vis–NIR absorption spectroelectrochemistry, and theoretical calculations are presented. This work attempts to unify the properties of different series of diradicaloids in a common argument as well as the properties of the carbocations and carbanions derived from them.

The synthesis and optoelectronic properties of 24 π-electron, formally antiaromatic fluoreno[3,2-b]fluorene and fluoreno[4,3-c]fluorene (FF), are presented. The solid-state structure of [4,3-c]FF along with computationally analogous molecules shows that the outer rings are aromatic while the central four rings possess a bond-localized 2,6-naphthoquinodimethane motif. The antiaromaticity and biradical character of the FFs is assessed computationally, the results of which indicate the dominance of the closed-shell ground state for these molecules.

Addressing the instability of antiaromatic compounds often involves protection with bulky groups and/or fusion of aromatic rings, thus decreasing paratropicity. We report four naphthothiophene-fused s-indacene isomers, one of which is more antiaromatic than parent s-indacene. This surprising result is examined computationally through nucleus-independent chemical shift XY calculations and experimentally via nuclear magnetic resonance spectroscopy, X-ray crystallography, ultraviolet−visible spectrophotometry, and cyclic voltammetry, with the latter two indicating that this molecule possesses the lowest highest occupied molecular orbital−lowest unoccupied molecular orbital energy gap observed for heterocycle-fused sindacene.

Rationally designed phosphaquinolinone derivatives containing electron-donating and/or -withdrawing groups are reported, with dimerization constants up to 525 M−1.

We examine the effects of fusing two benzofurans to s-indacene (indacenodibenzofurans,I DBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units.S ynthesis via 3-functionalized benzofuran yields syn-IDBF and syn-IIDBF.s yn-IDBF possesses ah igh degree of paratropicity,e xceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn-IIDBF.I nt he case of the anti-isomers, synthesized via 2-substituted benzofurans,t hese effects are decreased;h owever,b oth derivatives undergo an unexpected ring-opening reaction during the final dearomatization step. All the results are compared to the benzothiophene-fused analogues and showt hat the increased electronegativity of oxygen in the syn-fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity.F or syn-IIDBF increased diradical character results from rearomatization of the core naphthalene unit in order to relieve this paratropicity.

We describe two novel hybrid receptors combining ap hosphorus-/nitrogen-containing (PN) phosphonamidate heterocycle with urea recognition units in an arylethynyl backbone.Structural, spectroscopic and computational studies reveal that the origin of superior binding for hydrogen sulfate (HSO 4 À )a nion is correlated with the formation of strong hetero-complementary hydrogen bonds with the phosphonamidate motif.W ef urther demonstrate that the hybrid host system is capable of capturing/transporting the HSO 4 À anion from an aqueous,b iphasic system. Selective detection and recognition of various anions haveattracted substantial attention. [1] Hydrogen sulfate (bisulfate, HSO 4 À )i so fc onsiderable interest owing to its concern as ac ontaminant in agricultural and industrial fields. [2] This hydroxyanion is am oderate acid (pK a % 2.0) [3] and is abundant in aqueous sulfuric acid and salt solutions.M eanwhile, the important sulfate (SO 4 2À )a nion will equilibrate with bisulfate ions in low pH environment. Hydrogen sulfate is the most prevalent inorganic component in lower and upper atmospheric aerosols and plays ar ole in aerosol homogeneous nucleation. [4] Additionally,t he HSO 4 À anion can also act as an important and effective catalyst for various chemical transformations. [5] As aresult, the design and development of various artificial host molecules for HSO 4 À anion binding has become ahighly desirable target in supramolecular chemistry.Unfortunately,d evelopment of synthetic receptors that are capable of selective recognition and binding toward HSO 4 À has proven challenging because of its H-bonding donor/acceptor nature as well as its unique tetrahedral geometry. [6] Over the past few decades,o nly ah andful of selective receptors for HSO 4 À have been documented. [7,8] These molecular systems are mainly composed of the wellknown acidic (N À H, O À H) and/or neutral (C À H) hydrogen bond (HB) donors and basic nitrogen atoms (such as amine, imine,imidazole,orpyridine motifs) [7] or carbonyl [8] motifs as the perceived HB accepting sites.T he resulting multidentate and/or macrocyclic architectures with convergent and complementary HB contacts typically give rise to strong anion binding affinities in solution phase,a lthough selectivity is often far from optimum. Furthermore,stabilization of HSO 4 À by complexation with receptors bearing basic moieties in the solid state has always been challenging since the protic oxyanion is susceptible to proton transfer to the host molecules. [7b,d] Hydroxyanions including HSO 4 À are wellknown to dimerize by forming anti-electrostatic, self-complementary (O À H) anion ···O anion hydrogen bonds in crystal structures, [9,10] or are prone to undergo proton transfer to generate SO 4 2À ion, [11] both of which would facilitate the electrostatic contacts with the HB donors due to the pronounced and unitary negative charge density.A saconsequence,t hese competitive processes make co-crystallization of host-guest complexes involving HSO 4 À asignificant challenge.Asearc...

The syntheses, molecular structures, reactivities, and computational assessment of dipotassium diboratapentacene isomers are described (1 and 2). These compounds represent the first examples of aromatized diboraacenes where the boron atoms are spatially separated in different rings of the acene framework. Both 1 and 2 react with carbon dioxide (CO2) via diastereoselective carboxylation of the pentacene backbone that likely proceeds by a frustrated Lewis pair-like mechanism. The placement of the boron atoms and the reactivity studies provide a platform for later stage functionalization of diboraacenes beyond the central ring of the polycyclic aromatic hydrocarbon core.