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This paper presents the use of O,S-acetals in a new modification of the oxo-Friedel–Crafts–Bradsher cyclization. In this reaction, under mild reaction conditions (25 °C), three- and four-ring fused RO-acenes (major) and/or HO(CH2)2S-acenes (minor) are formed, the latter products having never been observed before in this type of cyclization. In this way, two electronically different fluorophores could be obtained in a single cyclization reaction, one of them having strong electron donor properties (+M effect of alkoxy groups) and the other having donor-acceptor properties (+M and −I effects of the HO(CH2)2S-group, Hammett's constants). Further increasing the reaction temperature, HCl concentration or prolonging reaction time, surprisingly, yielded a 2:1 mixture of cis and trans dimeric isomers, as the only products of this cyclization. The DFT calculations confirmed a greater stability of the cis isomer compared to the trans isomer. The formation of unexpected dimeric products and HO(CH2)2S-acenes sheds light on the mechanism of oxo-Friedel–Crafts–Bradsher cyclization, involving competitive O/S atom protonation in strained O,S-acetals and in strain-free side groups of intermediate species. [ABSTRACT FROM AUTHOR]

N -heterocycles are suspected to play an important role in the chemical origin of life. Despite their detection in meteorites and in Titan's atmosphere, their extra-terrestrial chemical formation networks remain elusive. Furthermore N -heterocyclics are undetected in the interstellar medium. This paper assesses the photostability of protonated N -hetero(poly)acenes after ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. It provides information on their ability to retain the N atom into the cycle to generate larger N -containing species or functionalized N -heterocyles. Protonated N -hetero(poly)acenes were generated using electrospray ionization and injected into a linear ion trap where they were irradiated by radiation of 4.5 to 10 eV using the DESIRS beamline at the synchrotron SOLEIL. The photodissociation action spectra of protonated pyridine, quinoline, isoquinoline, and acridine were measured by recording the photofragment yields as a function of photon energy. The four systems exhibit dissociation channels associated with H2 and HCN/HNC loss but with different branching ratios. The results indicate that increasing the size of the N -hetero(poly)acenes increases the chance of retaining the N atom in the larger fragment ion after photodissociation but it remains that all the protonated N -hetero(poly)acenes studied lose their N atom at part of a small neutral photofragment, with high propensity. Therefore, protonated N -hetero(poly)acenes in interstellar space are unlikely precursors to form larger N -containing species. However, protonated pyridine, quinoline, isoquinoline, and acridine are most likely to retain their N atoms in planetary atmospheres where UV radiation at the planet's surface is typically restricted to wavelengths greater than 200 nm – suggesting such environments are possible substrates for prebiotic chemistry. [ABSTRACT FROM AUTHOR]

For the structure–property modeling of thermodynamic properties of polycyclic aromatic hydrocarbons (PAHs), this paper explores the effectiveness of a specific class of graphical indices defined based on eigenvalues, also known as valency-spectral graphical indices. The 30 lower PAHs have been selected as test molecules. The heat capacity (C p) and entropy (S o) are the standard choices for characterizing thermodynamic properties due to their close correlation with the thermodynamic properties of a similar nature. A computer-dependent method is proposed to calculate valency-spectral indices of chemical graphs, and it is employed to compute the indices for our test molecules. The statistical inferences reveal an unexpected finding for the Estrada harmonic energy, a less familiarized spectral descriptor within the research community, outperforming all the existing descriptors, followed by the positive & negative inertia indices. The Estrada harmonic energy achieved the highest mean correlation coefficient of ρ > 0. 99. On the other hand, well-studied descriptors such as Laplacian energy and adjacency energy still maintained their effectiveness in correlating the thermodynamic properties of PAHs; however, they were significantly outperformed by the Estrada harmonic energy. The three best valency-spectral indices are employed in the structure–property modeling of thermodynamic properties of linear polyacenes. [Display omitted] [ABSTRACT FROM AUTHOR]

Catacondensed benzenoids (those benzenoids having no carbon atom belonging to three hexagonal rings) form the simplest class of polycyclic aromatic hydrocarbons (PAH). They have a long history of study and are of wide chemical importance. In this paper, mathematical possibilities for natural extension of the notion of a catacondensed benzenoid are discussed, leading under plausible chemically and physically motivated restrictions to the notion of a catacondensed chemical hexagonal complex (CCHC). A general polygonal complex is a topological structure composed of polygons that are glued together along certain edges. A polygonal complex is flat if none of its edges belong to more than two polygons. A connected flat polygonal complex determines an orientable or nonorientable surface, possibly with boundary. A CCHC is then a connected flat polygonal complex all of whose polygons are hexagons and each of whose vertices belongs to at most two hexagonal faces. We prove that all CCHC are Kekulean and give formulas for counting the perfect matchings in a series of examples based on expansion of cubic graphs in which the edges are replaced by linear polyacenes of equal length. As a preliminary assessment of the likely stability of molecules with CCHC structure, all-electron quantum chemical calculations are applied to molecular structures based on several CCHC, using either linear or kinked unbranched catafused polyacenes as the expansion motif. The systems examined all have closed shells according to Hückel theory and all correspond to minima on the potential surface, thus passing the most basic test for plausibility as a chemical species. Preliminary indications are that relative energies of isomers are affected by the choice of the catafusene motif, with a preference shown for kinked over linear polyacenes, and for attachment by angular connection at the branching hexagons derived from the vertices of the underlying cubic structure. Avoidance of steric crowding of H atoms appears to be a significant factor in these preferences. [ABSTRACT FROM AUTHOR]

This review focuses on obtaining embedded azulene polycyclic molecules treated according to their particular structure. The division of material into the azulene unit grafted only on one or two bonds and poly-fused azulene compounds was suggested with the intention of facilitating the presentation and assimilation of information. The similarity of some structural features in the compounds included in different analyzed classes results in the presence of the same synthesis protocol in several places. Obtaining benz[a]azulenes, azulene-fused acenes, and helicenes or azulene-embedded nanographene, along with other compounds, is presented. [ABSTRACT FROM AUTHOR]

Photoluminescence effects in organic chromophores are of significant importance and requires precise description of low lying excited states. In this communication, we put forward an alternative time‐independent DFT scheme for computing lowest single‐particle excitation energy, especially for singlet excited state. This adopts a recently developed "virial"‐theorem based model of singlet‐triplet splitting which requires a DFT calculation on closed shell ground state and a restricted open‐shell triplet excited state, followed by a simple 2e- integral evaluation. This produces vertical excitation energies in small molecules, linear and non‐linear polycyclic aromatic hydrocarbon and organic dyes in comparable accuracy to the TDDFT. We also explore the functional dependency of present method with three different functionals (B3LYP, wB97X and CAM‐B3LYP) for polyenes and linear acenes. A systematic comparison with literature value illustrates the validity and usefulness of the present scheme in determining optical gap with fair computational cost. [ABSTRACT FROM AUTHOR]

The electronic and optical responses of an organic semiconductor (OSC) are dictated by the chemistries of the molecular or polymer building blocks and how these chromophores pack in the solid state. Understanding the physicochemical nature of these responses is not only critical for determining the OSC performance for a particular application, but the UV/visible optical response may also be of potential use to determine aspects of the molecular-scale solid-state packing for crystal polymorphs or thin-film morphologies that are difficult to determine otherwise. To probe these relationships, we report the quantum-chemical investigation of a series of trialkyltetrelethynyl acenes (tetrel = silicon or germanium) that adopt the brickwork, slip-stack, or herringbone (HB) packing configurations; the π-conjugated backbones considered here are pentacene and anthradithiophene. For comparison, HB-packed (unsubstituted) pentacene is also included. Density functional theory and G0W0 (single-shot Green's function G and/or screened Coulomb function W) electronic band structures, G0W0-Bethe–Salpeter equation-derived optical spectra, polarized ϵ2 spectra, and distributions of both singlet and triplet exciton wave functions are reported. Configurational disorder is also considered. Furthermore, we evaluate the probability of singlet fission in these materials through energy conservation relationships. [ABSTRACT FROM AUTHOR]

Singlet fission (SF), a process that produces two triplet excitons from one singlet exciton, has attracted recent interest for its potential to circumvent the detailed-balance efficiency limit of single-junction solar cells. For the potential of SF to be fully realized, accurate assignment and quantification of SF is necessary. Intersystem crossing (ISC) is another process of singlet to triplet conversion that is important to distinguish from SF to avoid either over- or under-estimation of SF triplet production. Here, we quantify an upper bound on the rate of ISC in two commonly studied SF chromophores, TIPS–pentacene and TIPS–tetracene, by using transient absorption spectroscopy of solutions of varying concentrations in toluene. We show that SF in solutions of these acenes has previously been misidentified as ISC, and vice versa. By determining a bimolecular SF rate constant in concentrated solutions in which SF dominates over ISC, we distinguish triplet formation due to SF from triplet formation due to ISC and show that the characteristic time scale of ISC must be longer than 325 ns in TIPS–pentacene, while it must be longer than 118 ns in TIPS–tetracene. We additionally note that no excimer formation is observed in the relatively dilute (up to 8 mM) solutions studied here, indicating that previous excimer formation observed at much higher concentrations may be partially due to aggregate formation. This work highlights that an accurate quantification of ISC is crucial as it leads to accurate determination of SF rate constants and yields. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence spectra and excitation lifetimes of anthracene, tetracene, and pentacene molecules attached to the surface of solid argon clusters have been measured with respect to cluster size, density of molecules, and excitation density. Results are compared to previous studies on the same sample molecules attached to neon clusters. A contrasting lifetime behavior of anthracene on neon and argon clusters is discussed, and mechanisms are suggested to interpret the results. Although both neon and argon clusters are considered to be weakly interacting environments, we find that the excitation decay dynamics of the studied acenes depends significantly on the cluster material. Moreover, we find even qualitative differences regarding the dependence on the dopant density. Based on these observations, previous assignments of collective radiative and non-radiative decay mechanisms are discussed in the context of the new experimental findings. [ABSTRACT FROM AUTHOR]

The functionalization of the aromatic backbone allows the improvement of the electrical properties of acene molecules in the amorphous layered structures of organic thin films. In the present work, we discuss the electric properties of the stable, amorphous, vacuum-deposited films prepared from five highly substituted 10-RO-acenes of various electronic properties, i.e., two extreme electron-donor (1,3-dioxa-cyclopenta[b]) anthracenes with all RO substituents, two anthracene carbaldehydes and one benzo[b]carbazole carbaldehyde possessing both electron-donor and acceptor substituents. The hole mobility data were obtained using subsequent steady state space charge limited currents (SCLC) and Time of Flight (TOF) measurements, performed on the same sample and these were then compared with the results of theoretical hole mobility calculations obtained using the Density Functional Theory (DFT) quantum—chemical calculations using the Marcus–Hush theory. The study shows a good agreement between the theoretical and experimental values which allows for the quick and quantitative estimation of Einstein's mobility values for highly substituted 10-RO anthracene and benzo[b]carbazole based on chemical calculations. This agreement also proves that the transport of holes follows the hopping mechanism. The theoretical calculations indicate that the reorganization energy plays a decisive role in the transport of holes in the amorphous layers of highly substituted hetero(acenes). [ABSTRACT FROM AUTHOR]

Here, we present a concise model that can predict the photoluminescent properties of a given compound from first principles, both within and beyond the Franck–Condon approximation. The formalism required to compute fluorescence, Internal Conversion (IC), and Inter-System Crossing (ISC) is discussed. The IC mechanism, in particular, is a difficult pathway to compute due to difficulties associated with the computation of required bosonic configurations and non-adiabatic coupling elements. Here, we offer a discussion and breakdown on how to model these pathways at the Density Functional Theory (DFT) level with respect to its computational implementation, strengths, and current limitations. The model is then used to compute the photoluminescent quantum yield (PLQY) of a number of small but important compounds: anthracene, tetracene, pentacene, diketo-pyrrolo-pyrrole (DPP), and Perylene Diimide (PDI) within a polarizable continuum model. Rate constants for fluorescence, IC, and ISC compare well for the most part with respect to experiment, despite triplet energies being overestimated to a degree. The resulting PLQYs are promising with respect to the level of theory being DFT. While we obtained a positive result for PDI within the Franck–Condon limit, the other systems require a second order correction. Recomputing quantum yields with Herzberg–Teller terms yields PLQYs of 0.19, 0.08, 0.04, 0.70, and 0.99 for anthracene, tetracene, pentacene, DPP, and PDI, respectively. Based on these results, we are confident that the presented methodology is sound with respect to the level of quantum chemistry and presents an important stepping stone in the search for a tool to predict the properties of larger coupled systems. [ABSTRACT FROM AUTHOR]

A zwitterionic open‐shell singlet diradical composed of electron‐donating anion, anthroxide, and electron‐accepting cation, phenazinium, was designed and synthesized. The diradical has a small HOMO–LUMO energy gap and shows near‐infrared absorption. Temperature‐dependent ESR measurements confirmed its small energy gap between ground singlet and thermally‐excited triplet states (ΔEST). The ΔEST of the diradical was changed by solvents (toluene, 2‐MeTHF, and EtOH). [ABSTRACT FROM AUTHOR]

The unsubstituted acenium radical cations (ARCs) are extremely sensitive and were hitherto only studied in situ, i. e. in the gas phase, as dilute solutions in strong acids or by matrix isolation spectroscopy at about 10 K. In this study, room temperature stable ARC salts with the weakly coordinating anion [F{Al(ORF)3}2]− (ORF=−OC(CF3)3) supported by the weakly coordinating solvent 1,2,3,4‐tetrafluorobenzene (TFB) were prepared and structurally, electrochemically and spectroscopically characterized. Reaction of the neutral acenes with Ag+[F{Al(ORF)3}2]− led, non‐innocent,[54] to intermediate [Ag2(acene)2]2+ complexes, which decompose over time to Ag0 and the corresponding (impure) ARC salts. By contrast, direct deelectronation with the recently developed innocent[54] deelectronator radical cation salt [anthraceneHal]+⋅[F{Al(ORF)3}2]− led to phase‐pure products [acene]+⋅[F{Al(ORF)3}2]− (anthraceneHal=9,10‐dichlorooctafluoroanthracene; acene=anthra‐, tetra‐, pentacene). For the first time, a homogenous set of spectroscopic data on analytically pure ARC salts was obtained. In addition, cyclovoltammetric measurements of the acenes connected the potentials in solution with those in the gas‐phase. Hence, the data complement the existing isolated gas‐phase, strong acid or matrix isolation studies. A first entry to follow‐up chemistry of the acenium radical cations as ligand forming oxidizers was demonstrated by reaction with 1/2 ${{ 1/2 }}$ Co2(CO)8 giving [Co(anthracene)(CO)2]+. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic endoperoxides are important sources of singlet oxygen (1O2) and their formation from polyacenes is well established. Anthracene carboxyimides are of particular interest as they exhibit excellent antitumor activity and possess unique photochemical properties. However, the photooxygenation of the synthetically versatile anthracene carboxyimide moiety has not been reported due to its competing [4+4] photodimerization reaction. Herein, we describe the reversible photo‐oxidation of an anthracene carboxyimide. X‐ray crystallographic analysis surprisingly revealed the formation of a racemic mixture of chiral hydroperoxides, rather than the expected endoperoxide. The photoproduct undergoes both photo‐ and thermolysis to form 1O2. Activation parameters were derived for the thermolysis and the mechanisms of photooxygenation and thermolysis are discussed. The anthracene carboxyimide also showed high selectivity and sensitivity for nitrite anions in acidic aqueous media and possessed stimuli‐responsive behaviour. [ABSTRACT FROM AUTHOR]

Besides the peripheral modification, the introduction of heteroatoms to modulate the property of longer acenes with improved chemical stability has been extensively studied for their potential applications in organic electronics. However, the utilization of 4‐pyridone, a common unit in the air‐ and photo‐stable acridone and quinacridone, to decorate higher acenes with increased stability has not been realized yet. Here we present the synthesis of a series of monopyridone‐doped acenes up to heptacene via the palladium‐catalyzed Buchwald‐Hartwig amination of aniline and dibromo‐ketone. The effect of pyridone on the property of doped acenes were investigated experimentally and computationally. With the π‐extension of doped acenes, the pyridone ring shows the weakened conjugation and gradual loss of aromaticity. The doped acenes demonstrate enhanced stability in solution and maintain the electronic communication between the acene planes. [ABSTRACT FROM AUTHOR]

Hydrocarbons with open-shell singlet and triplet ground states have long been studied. In contrast to studies of Kekulé hydrocarbons with an open-shell singlet ground state, studies of non-Kekulé and Kekulé hydrocarbons with a triplet ground state are quite limited, and no hydrocarbon with a triplet ground state has been isolated as single crystals. In this review, our work on the synthesis, isolation, and properties of m-quinodimethane-based non-Kekulé polycyclic hydrocarbon, a kinetically stabilized triangulene derivative, and Kekulé polycyclic hydrocarbon, a kinetically stabilized bisdibenzo[3,4:5,6]cyclohepta[1,2-a:2,1-d]benzene derivative, are described. Triplet ground states of these hydrocarbons were experimentally confirmed by ESR and magnetic measurements, and these are the first example of polycyclic hydrocarbons with a triplet ground state whose structures were characterized by X-ray crystal structural analysis. These studies will enable the development of various polycyclic hydrocarbon multi-radicals with high spin multiplicity. [ABSTRACT FROM AUTHOR]

A strongly twisted benzo‐fused tris‐cycloheptenylene, containing three dibenzosuberenone units fused to a common benzene ring, was subjected to Ramirez olefination and subsequent palladium‐catalyzed Suzuki‐Miyaura cross‐coupling with 4‐substituted phenylboronic acids. The high steric demand within the overcrowded, benzene‐rich benzo‐fused tris‐cycloheptenylenes enforced an unprecedented 1,2‐rearrangement upon π‐extension during the Suzuki coupling reaction. According to crystal structure analysis, the resulting negatively curved polycyclic aromatic hydrocarbons consist of two heptagons and one octagon surrounding a central benzene ring as a result of strain release. In the solid state, the materials exhibit a blue to blue‐green fluorescence with increased quantum yields and a hypsochromic shift of the emission maxima compared to their respective solutions. [ABSTRACT FROM AUTHOR]

A simplified form of the Bixon–Jortner–Plotnikov (BJP) method is derived for calculation of internal conversion (IC) rate in a symmetrical molecule. The rate is a sum of contributions from individual transitions between vibronic states. For each transition, vibrational modes are divided into two groups, the promoting (one or two modes per electronic transition) and the surrounding ones. In the case of the non-totally symmetric transition in a symmetric molecule, the overwhelming majority of transitions do not contribute to the overall rate. Moreover, the promoting and surrounding modes belong to different symmetry representations and can be separated. It is proposed to deal with the promoting modes directly, while approximating the effect of the surrounding modes by a Pekarian function. The method was tested on polyacenes and it was shown that the calculated IC rates are in agreement with the experimental ones. The simplified method can be applied for calculating the rates of non-totally symmetric transition in a symmetric molecule, if its point symmetry group does not change after transition. [ABSTRACT FROM AUTHOR]

Non‐alternant non‐benzenoid π‐conjugated polycyclic hydrocarbons (PHs) are expected to exhibit very different electronic properties from the all‐benzenoid PHs. Herein, we report the synthesis and physical properties of three azulene‐fused acene molecules (1, 2 and 3), which are isoelectronic to the pentacene, hexacene and heptacene, respectively. X‐ray crystallographic analysis, NMR spectra, and theoretical calculations reveal a localised aromatic backbone comprising all the six‐ and five‐membered rings while the seven‐membered ring remains non‐aromatic. They display properties of both azulene and acenes and are much more stable than the respective acenes. The dications of 1, 2 and 3 were formed by chemical oxidation. Notably, 32+ exhibited an open‐shell diradical character (y0=30.2 %) as confirmed by variable‐temperature NMR and ESR measurements, which can be explained by recovery of aromaticity of an 2,6‐anthraquinodimethane unit annulated with two aromatic tropylium rings. [ABSTRACT FROM AUTHOR]

In this study, we describe a synthetic method for incorporating arenes into closed tubes that we name capsularenes. First, we prepared vase‐shaped molecular baskets 4–7. The baskets comprise a benzene base fused to three bicycle[2.2.1]heptane rings that extend into phthalimide (4), naphthalimide (6), and anthraceneimide sides (7), each carrying a dimethoxyethane acetal group. In the presence of catalytic trifluoroacetic acid (TFA), the acetals at top of 4, 6 and 7 change into aliphatic aldehydes followed by their intramolecular cyclization into 1,3,5‐trioxane (1H NMR spectroscopy). Such ring closure is nearly a quantitative process that furnishes differently sized capsularenes 1 (0.7×0.9 nm), 8 (0.7×1.1 nm;) and 9 (0.7×1.4 nm;) characterized by X‐Ray crystallography, microcrystal electron diffraction, UV/Vis, fluorescence, cyclic voltammetry, and thermogravimetry. With exceptional rigidity, unique topology, great thermal stability, and perhaps tuneable optoelectronic characteristics, capsularenes hold promise for the construction of novel organic electronic devices. [ABSTRACT FROM AUTHOR]

Solar energy is widely used as a renewable and clean energy, and how to improve the photovoltaic conversion efficiency of solar devices has always been a hot topic. Singlet fission (SF), which converts one singlet exciton into two triplet excitons, is an exciton multiplication generation process in organic semiconductors and is expected to be integrated into solar cells. Moreover, acenes are currently one of the most widely used and popular SF materials. We review recent research on novel acene materials and their developments in the field of solar cells, aiming to provide researchers with ideas for applying the SF process to solar cells. [ABSTRACT FROM AUTHOR]

This comprehensive review, covering the years 1968–2022, is not only a retrospective investigation of a certain group of linearly fused aromatics, called acenes, but also a presentation of the current state of the knowledge on the synthesis, reactions, and applications of these compounds. Their characteristic feature is substitution of the aromatic system by one, two, or three organophosphorus groups, which determine their properties and applications. The (PIII, PIV, PV) phosphorus atom in organophosphorus groups is linked to the acene directly by a P-Csp2 bond or indirectly through an oxygen atom by a P-O-Csp2 bond. [ABSTRACT FROM AUTHOR]

A group of aromatic compounds (benzene, naphthalene, anthracene, and tetracene) was selected to design four sheets of graphene based on quantum mechanics calculations using the density function theory (DFT), leaning on the cyclic polymerization mechanism. Theoretical results offer that graphene-I is the most stable depending on the values of EHOMO (− 4.91601 eV), gap energy (2.76549 eV), and total energy (− 3447.42377654 a.u.). The thermodynamic theoretical outcome showed that all reactions are exothermic and spontaneous. Graphene is a two-dimensional plane, so the nanotube design process is with two possibilities: the first about the x-axis (horizontal (H)) and the second about the y-axis (vertical (V)). The theoretical results gave two groups: the first gave more stability to graphene at the expense of the nanotubes prepared from it, namely, graphene-I and the second gave less stability to graphene compared to the nanotubes prepared from it, namely, graphene-II, graphene-III, and graphene-IV), depending on the energy of HOMO and gap energy. The value of gap energy ranged (from 1.10370 to 1.79922 eV) for the following compounds (graphene-II, nanotube-II-V, nanotube-III-H, and nanotube-IV-V), making those important compounds in solar cells. These theoretical results showed the possibility of preparing graphene and then nanotubes from aromatic compounds, giving the benefit of doubling the preparation of new compounds with important applications and at the same time eliminating aromatic compounds harmful to the environment. [ABSTRACT FROM AUTHOR]

Harvesting long-lived free triplets in high yields by utilizing organic singlet fission materials can be the cornerstone for increasing photovoltaic efficiencies potentially. However, except for polyacenes, which are the most studied systems in the singlet fission field, spin-entangled correlated triplet pairs and free triplets born through singlet fission are relatively poorly characterized. By utilizing transient absorption and photoluminescence spectroscopy in supramolecular aggregate thin films consisting of Hamilton-receptor-substituted diketopyrrolopyrrole derivatives, we show that photoexcitation gives rise to the formation of spin-0 correlated triplet pair 1(TT) from the lower Frenkel exciton state. The existence of 1(TT) is proved through faint Herzberg-Teller emission that is enabled by vibronic coupling and correlated with an artifact-free triplet-state photoinduced absorption in the near-infrared. Surprisingly, transient electron paramagnetic resonance reveals that long-lived triplets are produced through classical intersystem crossing instead of 1(TT) dissociation, with the two pathways in competition. Moreover, comparison of the triplet-formation dynamics in J-like and H-like thin films with the same energetics reveals that spin-orbit coupling mediated intersystem crossing persists in both. However, 1(TT) only forms in the J-like film, pinpointing the huge impact of intermolecular coupling geometry on singlet fission dynamics. The singlet fission mechanism is still not relatively well understood, except for polyacenes. Here, the authors demonstrate that in diketopyrrolopyrrole supramolecular assemblies, both singlet fission and intersystem crossing can simultaneously happen. [ABSTRACT FROM AUTHOR]

Buchwald‐Hartwig coupling of a triisopropylsilyl (TIPS)‐ethynylated dibromo‐N,N'‐dihydrotetraazapentacene with 1,4‐bis(TIPS‐ethynyl)‐2,3‐diaminonaphthalene furnishes a dihydrohexaazaoctacene. Its oxidation with MnO2 results in a 7,7'‐bi(hexaazaoctacenyl). In addition to eight TIPS‐ethynyl groups, the bioctacene motif protects the azaoctacene subunits. The biazaoctacenyl displays a τ1/2 of > 5 d in dilute solution under ambient conditions. In the crystalline state it is persistent for > 10 months. [ABSTRACT FROM AUTHOR]

Anthracene (C14H10) and its derivatives, π‐conjugated molecules in acenes, have been widely researched in terms of their reactions, physical properties, and self‐assembly (or crystal engineering). These molecules can be functionalized to tune reactivities, optoelectronic properties, and self‐assembling abilities. Structural changes in the molecular assemblies, solid states, and crystals have recently been discovered. Therefore, a systematic discussion of anthracene's molecular structure, packing, and optical properties based on its intermolecular structure and phase transitions is important for future chemical and structural design. In the present review, we discuss anthracene's molecular design, dimer packing, and crystal structure, focusing on the structural phase transitions of its crystals. We also provide examples of the phase transitions of anthracene crystals. Changes to edge‐to‐face of CH‐π interaction and face‐to‐face packing of π‐π interaction affect the thermodynamic stabilities of various crystal structures. These structures can inform the prediction of structural and physical properties. [ABSTRACT FROM AUTHOR]

A modular approach to azulene building blocks was developed starting from readily available aryl‐substituted cyclopentadiene and ortho‐haloaryl aldehyde by dehydration condensation followed by palladium‐catalyzed C−H coupling. It facilitates the synthesis of four nonalternant isomers of pentacene and hexacene, namely, dibenzo[e,g]azulene, benzo[1,2‐f : 5,4‐f′]diazulene, benzo[1,2‐f : 4,5‐f′]diazulene, and naphtho[2,3‐f : 6,7‐f′]diazulene, which exhibit narrow band gaps with high stability in addition to protonation‐caused enhanced near‐infrared fluorescence. We discovered that in these isomers, i) constitutional isomerism influences significantly their photoelectric properties and ii) the elongation of the conjugation system does not necessarily lead to a narrowing in the band gap. Due to the easy modifiability of the nonazulene building blocks, this strategy can be extended to modularly prepare numerous multiazulene‐fused aromatics. [ABSTRACT FROM AUTHOR]

We report the straightforward one‐pot synthesis of novel 5‐ or 6‐membered P‐heterocycles featuring an internal ylidic bond: P‐containing acenaphthylenes and phenanthrenes. The stability of the compounds tolerates post‐functionalization through direct arylation to introduce electron‐rich/poor substituents and the synthetic strategy is also compatible with the preparation of more elaborate polyaromatic scaffolds such as acenes and helicenes. Using a joint experimental (X‐ray analysis, optical and redox properties) and theoretical approach, we perform a full structure–property relationships study on these new platforms. In particular, we show that molecular engineering allows not only tuning their absorption/emission across the entire visible range but also endowing them with chiroptical or non‐linear optical properties, making them valuable dyes for a large panel of photonic or opto‐electronic applications. [ABSTRACT FROM AUTHOR]

Sixfold TIPS‐ethynylation combined with fourfold bromination of the armchair edges furnishes a long‐lived, soluble heptacene; π‐extension via Stille coupling accesses a persistent tetrabenzononacene. Both types of acenes were stabilized best by double TIPS‐ethynylation on every other benzene ring. Tetrabromoheptacene is an ambipolar transistor material (up to 0.036 cm2 V−1 s−1 n‐channel), which was corroborated by generation of its monoanion and monocation. [ABSTRACT FROM AUTHOR]

This paper presents the use of O,S-acetals in a new modification of the oxo-Friedel–Crafts–Bradsher cyclization. In this reaction, under mild reaction conditions (25 °C), three- and four-ring fused RO-acenes (major) and/or HO(CH2)2S-acenes (minor) are formed, the latter products having never been observed before in this type of cyclization. In this way, two electronically different fluorophores could be obtained in a single cyclization reaction, one of them having strong electron donor properties (+M effect of alkoxy groups) and the other having donor-acceptor properties (+M and −I effects of the HO(CH2)2S-group, Hammett’s constants). Further increasing the reaction temperature, HCl concentration or prolonging reaction time, surprisingly, yielded a 2:1 mixture of cis and trans dimeric isomers, as the only products of this cyclization. The DFT calculations confirmed a greater stability of the cis isomer compared to the trans isomer. The formation of unexpected dimeric products and HO(CH2)2S-acenes sheds light on the mechanism of oxo-Friedel–Crafts–Bradsher cyclization, involving competitive O/S atom protonation in strained O,S-acetals and in strain-free side groups of intermediate species.

Boron‐embedded heteroacenes (boraacenes) have attracted enormous interest in organic chemistry and materials science. However, extending the skeleton of boraacenes to higher acenes (N≥6) is synthetically challenging because of their limited stability under ambient conditions. Herein, we report the synthesis of boron‐embedded heptacene (DBH) and nonacene (DBN) as the hitherto longest boraacenes. The former is highly stable (even after 240 h in tetrahydrofuran), while the latter is air‐sensitive with the half‐life (t1/2) of 11.8 min. The structures of both compounds are verified by single‐crystal X‐ray diffraction, revealing a linear backbone with an antiaromatic C4B2 core. Photophysical characterizations associated with theoretical calculations indicate that both compounds exhibit highly efficient anti‐Kasha emissions. Remarkably, the air‐stable DBH manifests an ultrahigh photoluminescence quantum yield (PLQY) of 98±2 % and can be chemically reduced to its radical anion and dianion states, implying the value of boron‐doped higher acenes as novel functional materials. [ABSTRACT FROM AUTHOR]

Hybrid polyaromatic hydrocarbons (PAHs) consisting of helicene and acene domains, referred to as [7]heli‐D‐acenes, are introduced as scaffolds to generate enantiopure twisted acenes (heli‐twistacenes) by a torque, lock, and propagate (TLP) approach. Computational methods with and without dispersion corrections were used to explore the structural and electronic features of these PAHs and to explore the possible formation of twistomers that might complicate reaction mixtures. Syntheses of unsubstituted and disubstituted members of the [7]heli‐D‐acene series confirmed the viability of the TLP approach, and together with the computational results, provided proof‐of‐concept of this new approach as a viable means to generate enantiopure twisted‐acenes. The X‐ray structures, absorption, fluorescence, phosphorescence, and CD spectra of these first generation heli‐acenes are compared to the structure and photophysical properties of pentacene and [7]helicene. A high barrier for the enantio‐enriched M enantiomer of 19,24‐dicyano[7]heli‐D‐anthracene verified its configurational stability at room temperature. [ABSTRACT FROM AUTHOR]

The surface of poly(ethylene terephthalate) (PET) films crystallizes when exposed to a broad class of organic solvents (protic polar, aprotic polar, and non‐polar). This phenomenon leads to irreversible changes in transparency and mechanical properties. It also limits PET films and coatings in applications including electronics, medicine, packaging, and construction. This work describes a method to impart solvent resistance to the PET surface by depositing a silicate film. This coating enables many post‐functionalization options, including those that tune wettability or impart antifouling characteristics to the parent PET surface. It also endows PET surface resistance to organic solvent exposure without affecting the overall mechanical and optical properties of the PET. Additionally, the silicate layer improves the scratch resistance of PET surfaces. [ABSTRACT FROM AUTHOR]

Optoelectronic properties of molecular solids are important for organic electronic devices and are largely determined by the adopted molecular packing motifs. In this study, we analyzed such structure‐property relationships for the partially regioselective fluorinated tetracenes 1,2,12‐trifluorotetracene, 1,2,10,12‐tetrafluorotetracene and 1,2,9,10,11‐pentafluorotetracene that were further compared with tetracene and perfluoro‐tetracene. Quantum chemical DFT calculations in combination with optical absorption spectroscopy data show that the frontier orbital energies are lowered with the degree of fluorination, while their optical gap is barely affected. However, the crystal structure changes from a herringbone packing motif of tetracene towards a planar stacking motif of the fluorinated tetracene derivatives, which is accompanied by the formation of excimers and leads to strongly red‐shifted photoluminescence with larger lifetimes. [ABSTRACT FROM AUTHOR]

The properties of π-conjugated oligomers and polymers are commonly controlled by side group engineering, main chain engineering, or conformational engineering. The last approach is typically limited to controlling the dihedral angle around the interring single bonds to prevent loss of π-conjugation. Here we propose a different approach to conformational engineering that involves controlling the twist of the aromatic units comprising the backbone by using a tether of varying lengths. We demonstrate this approach by synthesizing an inherently twisted building unit comprised of helically locked tethered acenes, bearing acetylene end-groups to enable backbone extension, which was applied in a series of nine helical oligomers with varying backbone length and twist. We find that the optical and electronic properties of π-conjugated systems may be determined by the additive, antagonistic, or independent effects of backbone length and twist angle. The twisted oligomers display chiral amplification, arising from the formation of secondary helical structures. One approach to altering the properties of π-conjugated oligomers is conformational engineering, in which the degree of rotation around the bonds linking monomers is restricted. Here the authors apply the conformational engineering approach on individual monomers using tethers of varying lengths to twist the aromatic units, and study the effects of varying the angles. [ABSTRACT FROM AUTHOR]

During the last years we have witnessed progressive evolution of preparation of acenes with length up to dodecacene by on-surface synthesis in ultra-high vacuum or generation of acenes up to decacene in solid matrices at low temperatures. While these protocols with very specific conditions produce the acenes in amount of few molecules, the strategies leading to the acenes in large quantities dawdle behind. Only recently and after 70 years of synthetic attempts, heptacene has been prepared in bulk phase. However, the preparative scale synthesis of higher homologues still remains a formidable challenge. Here we report the preparation and characterisation of nonacene and show its excellent thermal and in-time stability. Acenes, or linearly fused benzene rings, have both fundamental scientific interest and potential for electronic and material utility, but synthesis of acenes with more than six rings are difficult due to dimerization and degradation. Here the authors prepare nonacene and demonstrate that it is stable in inert conditions. [ABSTRACT FROM AUTHOR]

The synthesis of novel (N−)acene‐based cyclooligomers is reported. Glaser‐Hay coupling of the bisethynylated monomers results in cyclodimers and cyclotrimers that are separable by column and gel‐permeation chromatographies. For the diazatetracene, the use of sec‐butyl‐silylethynyl groups is necessary to achieve solubility. Diazatetracene‐based cyclodimers and cyclotrimers were used as semiconductors in thin‐film transistors. Although their optoelectronic properties are quite similar, their electron mobilities in proof‐of‐concept thin‐film transistors differ by an order of magnitude. [ABSTRACT FROM AUTHOR]